ASHINGTON - Sixteen years ago, two Vietnam veterans, John F. Kerry and Al Gore, joined the elite club of the US Senate. They were a study in contrasts, the Southerner who opposed gun control and federal funding for abortion, and the New Englander who quickly became one of the Senate's most liberal members.
Over the years, the two men, both envisioning themselves as possible future presidents, both well-heeled Ivy Leaguers, watched each other warily, clashing on some issues, working together on others.
The clash nearly exploded: Last year, Kerry was uncertain enough about Gore that he almost challenged the vice president for the Democratic nomination.
But the bond between the two men, woven through common interests in the environment, technology and foreign affairs, has survived - and has remained strong enough that Gore has put Kerry at or near the top of his list of potential running mates.
Gore has said he will appear in Nashville with his running mate on Tuesday. Whether or not Kerry is picked, the search has highlighted the rivalry-turned-partnership of two ambitious Democrats.
The 1984 election, a landslide reelection of the Reagan-Bush ticket, was a disaster for many Democrats. But Gore and Kerry were among the survivors, and they viewed themselves as the future of the party.
From neighboring suites on the fourth floor of the Russell Office Building, the two joined forces on everything from arms control to veterans' benefits to the emerging world of computers and technology.
''There was an automatic camaraderie there, there was a start of a friendship that had a lot to do with them being in the same class where not many Democrats won that year,'' a Kerry associate said.
Vietnam linked the two veterans. Gore served as an Army journalist, reporting the war more than participating in it. Kerry found himself in the the thick of battle, serving as a highly decorated Navy officer aboard a gunboat.
But in other ways, the relationship was ideologically unsure. Gore, whose father had lost the Senate seat in 1970 after he was branded as too liberal, struck a much more conservative chord than is consistent with his current image.
Determined to avoid his father's fate, Gore earned a top rating from the National Rifle Association and opposed federal funding for abortion. These positions, said Bill Bradley, his chief primary opponent, showed Gore's real beliefs.
Kerry was quite the opposite. He embraced liberalism, as proudly and defiantly as he once worked with a group called Vietnam Veterans Against the War.
When Michael S. Dukakis ran for governor in 1982, with Kerry as running mate for lieutenant governor, some perceived Kerry as the more liberal of the two. Later, in 1988, Dukakis was tagged as a liberal, and lost to George Bush.
Within a year of their Senate arrival, Gore's and Kerry's directions seemed clear. In 1985, when Congressional Quarterly tabulated the 14 most important votes, the two senators agreed on 10 but disagreed on four revealing issues. Gore voted for, and Kerry against, these four measures: spending $1.5 billion to buy 21 mobile MX nuclear missiles; limiting contributions to the United Nations; relaxing many gun control laws; and further penalizing employers who had knowingly hired illegal immigrants.
The rankings of Gore and Kerry, as compiled by liberal and conservative groups, reflected those votes: Kerry agreed with the liberal Americans for Democratic Action 85 percent of the time, compared with 65 percent for Gore. Gore agreed with the American Conservative Union 17 percent of the time, compared with 5 percent for Kerry.
Still, Senator Paul Simon, the Illinois Democrat who also arrived in 1984, said Kerry and Gore got along well.
''The fact that you differ doesn't mean you don't have a good relationship,'' Simon said. ''I had a good relationship with Jesse Helms, for example.''
Both Kerry and Gore, like Simon himself, seemed to view themselves as presidential material, Simon said. But Kerry and Gore saw different paths.
Shortly after Gore arrived in the Senate, he became a cofounder of a group called the Democratic Leadership Council, which promotes a moderate ''New Democrat'' agenda. Another cofounder was Bill Clinton, then governor of Arkansas.
Kerry did not join at that time, council officials said.
It was not until the mid-1990s that Kerry, partly in response to the changing politics of the time, had changed his mind. Many factors led to Kerry's decision: the Dukakis defeat in 1988, the ascension of William F. Weld as governor of Massachusetts, and the success of the New Democrats Clinton and Gore in the election.
Kerry decided to join the club, and has become one of the most active members of the Democratic Leadership Council in the last few years, according to the council president, Al From.
''Kerry over the last four or five years has been almost as active as any other senator,'' From said. ''He has taken the lead on education policy for us.''
In recent years, Kerry has often said he has been misunderstood as a doctrinaire liberal. He has maintained that while he is on the left on some issues, his views in many areas defy classification. Kerry, for example, backed the Gramm-Rudman-Hollings deficit reduction bill during the Reagan administration, a position at odds with that of many liberal groups.
Kerry also opposed his usual allies in organized labor by backing free-trade deals, and he upset some teachers' groups by backing charter schools and the implementation of strict graduation standards.
By 1997, Kerry was a different sort of senator than when he had arrived. He voted with the American Conservative Union 16 percent of the time, compared with his 5 percent in 1985 and zero percent for Senator Edward M. Kennedy.
Kerry had become a bona fide New Democrat. And Gore and the rest of the Democratic Leadership Council crowd noticed.
''This liberal label stuff is silly,'' Dukakis said. ''John is a good, solid liberal Democrat, call him what you will; but he is also one to say that he doesn't agree with yesterday's liberal orthodoxy, and I'm not sure I agree with him all the time. It has nothing to do with moving to the center. I think it's a strength.''
Gore, meanwhile, was also evolving, moving away from some of his conservative positions, becoming a supporter of gun control laws and of federal funding for abortion, while remaining solidly in New Democrat territory on issues such as free trade.
By the time of the 1992 presidential race, Kerry and Gore had both changed; they had moved closer ideologically. The relationship was solidified by their work together on the environment, according to Marla Romash, a former Gore aide. In June 1992, the two traveled together to Brazil to attend the Earth Summit and to push for reductions in global warming.
But Kerry and Gore remained at odds on some issues. In 1991, in one of the most important votes of Gore's career, the Tennessean voted to support President Bush's request to use force in the Gulf War.
Kerry voted against the resolution. He said he wanted to give economic sanctions more time to work ''before rushing headlong into war.''
By some accounts, Gore's vote helped him secure the vice presidential spot. Bill Clinton had waffled on whether he would have voted for the use of force, and the governor of Arkansas was searching for a running mate with foreign policy experience who had backed the Gulf War.
Kerry's name came up in the initial search for a running mate, but he was not seriously considered, partly because of his voting record and his opposition to the Gulf War resolution. Indeed, Kerry's Gulf War vote has been a sore point with some Gore aides in the current process.
In any case, when the Clinton-Gore team took office, Kerry became one of the administration's most consistent supporters. In 1999, for example, Kerry and three other senators voted with the administration 93 percent of the time, the highest of any members of the US Senate.
Still, by late 1999, Kerry was seriously considering challenging Gore for the presidential nomination. It was partly a political question: Could Gore survive the country's disdain for Clinton's misconduct in the Oval Office, and would there ever be a better opportunity for Kerry to fulfill his ambition to be president?
In the end, the impeachment trial and the prospect of fighting an incumbent vice president for campaign cash and party loyalty put an end to the idea of challenging Gore. Moreover, ''John couldn't find the policy rationale to run against him,'' a Kerry associate said.
Shortly after Kerry made his decision, a source said, Gore called him up to ask: How would you have run against me?
The two agreed to meet at the vice president's mansion on the grounds of the Naval Observatory in March 1999. For two hours, they hashed out issues. Kerry outlined potential vulnerabilities for Gore and suggested courses of action. But mostly, it was ''a wonk-fest,'' said an aide who participated.
It was also the political equivalent of a peace conference, and the two agreed to work together. Gore and Kerry had never been intimate friends, but they shared a belief in the need to keep the White House in Democratic hands.
Kerry promised the vice president that he would vigorously campaign in New Hampshire, where many residents came from Massachusetts and were familiar with the senator.
In the ensuing months, as former senator Bill Bradley began mounting a serious challenge to Gore in New Hampshire, Gore consulted with Kerry on issues such as health care and education.
Still, as Gore pondered his choice of a running mate in recent weeks, some of his associates had a nagging worry: While they believed Kerry had changed from his dyed-in-the-wool liberal days into a New Democrat, they feared he would be instantly caricatured by Republicans as Dukakis's liberal lieutenant governor from Massachusetts.
It helped explain why some aides were pushing other New Democrats whose credentials would be less subject to challenge, such as Senator Joseph I. Lieberman of Connecticut or Senator John Edwards of North Carolina.
Gore, asked in a recent interview about whether he shares such concerns about Kerry, declined to say anything about his one-time Senate colleague.
''I'm not going to get into the personalities,'' Gore said, cutting off the discussion.
