ASHINGTON - When George W. Bush and Al Gore meet Tuesday in Boston for their first debate, one candidate will promote his agenda for cradle-to-grave government programs, and the other will urge that the surplus be used to pay off the national debt.
It is the opposite of what might be assumed. Bush, reaching for moderate support, is the one with the cradle-to-grave ''blueprint for the middle class,'' while Gore is pushing the conservative-sounding program to eliminate the debt.
Now, after months of molding their message toward the middle, Gore and Bush are carefully switching gears. They plan to use the Boston debate to draw the sharpest possible distinctions between their visions for America. But as they do so, they must struggle not to offend the moderates they have worked to attract. At the same time, each candidate is likely to portray his opponent as being out of the mainstream.
A clear victory in the debate could give a candidate a potentially decisive 3 percent or 4 percent bump in the polls, said Anthony Corrado, a Colby College professor who has studied the effect of debates on presidential elections.
''We will see both of them cast appeals to the middle class,'' said Corrado, author of ''Let America Decide,'' a book on presidential debates.
''I think they will tend not to be negative, particularly in this first debate. The tone will be, `I understand you, I understand what you care about.' We will hear a lot of stories about people they met on the campaign trail.''
In the 40-year history of televised debates, this will be the first general election encounter that occurs without the backdrop of either the Cold War or a budget deficit. The result is that this debate is likely to focus on the effect of the candidate's proposals on voters' everyday lives, down to the cost of prescription drugs, the price of gasoline and heating oil, and the quality of local schools.
If recent speeches are an indication, the debate may be dominated by a discussion of varying multibillion-dollar plans, as each candidate insists that his will provide more benefits. In recent days, for example, Bush and Gore have conducted a mini-debate over whose plan would be most beneficial to a 79-year-old Iowan who told Gore about how she collected soda cans to help pay for prescription drugs. Gore invited the woman, Winifred Skinner, to join him at the debate, but the Bush campaign hoped to turn the tables on the vice president by saying that the Texas governor's plan would provide more immediate relief to the woman.
With the debate taking place in the tightest presidential campaign in recent history, the mission of both candidates is to reassure their political base and to reach out to the 15 percent or so of voters who are undecided. That group, which largely accounts for recent wild swings in the polls, is weighted with independents, moderates, women, and suburbanites who may be turned off if a candidate seems too harsh or partisan.
Through their campaigns, Bush and Gore have seemed almost to have a tacit agreement about what they view as the biggest issues in this time of peace and prosperity: prescription drugs, education, and health care.
But the candidates also have left a raft of issues largely unspoken on the campaign trail, especially matters that are the concern of the most conservative or liberal wings of the party. The campaign has been more about practicalities and the pocketbook than an effort to underscore a large partisan ideological divide.
Neither Bush nor Gore, for example, has given a speech devoted solely to abortion since the primaries, even though that is one of their biggest disagreements. And little has been heard about the war on drugs or the need for inner-city housing.
Perhaps the most remarkable thing about Campaign 2000 is that both the Republican and Democratic candidates agree that some of the largest government programs should be expanded. Unlike in some past races, in which the Democrat typically advocated bigger programs and the Republican typically wanted to reduce them, Gore and Bush want to change and expand Medicare and federal aid to education, although they differ in details.
But the tone has changed as the candidates have laid the groundwork for the debate. Gore now casts himself as a populist warrior, fighting for ''people, not the powerful.'' Bush drew last week upon the 1988 rhetoric of his father, who castigated the Democratic nominee, Michael S. Dukakis, as a liberal. Gore, Bush said, has ''cast his lot with the old Democratic Party.''
''My opponent has left the vital center of American politics,'' Bush said.
Gore, meanwhile, has harrumphed at Bush's effort to portray himself as a ''compassionate conservative.'' Previewing his debate strategy, Gore presents himself as the more fiscally conservative, noting that he has a plan to eliminate the national debt while saying that Bush's tax cut would disproportionately aid the wealthiest 1 percent of Americans.
The biggest differences between the candidates are in the details. Bush wants to allow a portion of Social Security to be privately invested, while Gore wants to use part of the budget surplus to shore up the retirement program. Each candidate is likely to portray the other's proposals as too risky or too timid.
''Each of them may say, `Wait a minute, this guy is not the middle-of-the-road character as he has led us to believe,''' said Alan Schroeder, a Northeastern University journalism professor who has studied presidential debates.
But the differences this year are not nearly so large as the gap between candidates in past debates. There is nothing, for example, to compare to Ronald W. Reagan's opposition to new taxes and Walter F. Mondale's call for tax increases in 1984.
This year, both Bush and Gore want to cut taxes, although Bush wants a bigger cut. Both want to increase arms spending, although Bush wants to go further than Gore. And both men want to retain the Department of Education, and want to spend tens of billions of extra dollars on it. In the past several elections, the Republican candidate called for the elimination of the Department of Education.
Analysts interviewed for this story agreed on one key point about this debate: A harsh attack could backfire, especially among undecided independents whom both candidates are courting.
''In today's environment the best attack is one that doesn't seem that way,'' Republican pollster Frank Luntz said. ''You do it by asking a rhetorical question. If it seems like an attack it instantly loses credibility. The people watching will lose interest for the rest of the debate. This is the election year for finesse. The single most important word is finesse.''
In the end, this year's debates may be more focused on connecting with voters than scoring policy points. Bush has a reputation as an untested debater, while Gore is said to be stiff and dull. In fact, most analysts think both reputations are overblown, but Tuesday will be the first chance for many viewers to decide for themselves.
''Bush is not that bad at it and Gore is not that good at it,'' said Schroeder, author of ''Presidential Debates: Forty Years of High-Risk TV.'' As the book title suggests, a debate can turn on an image or an unscripted moment that no one can anticipate, such as President Gerald R. Ford's 1976 gaffe, in which he said Eastern Europe was not under Soviet domination.
Dukakis, whose less-than-stellar debate performance against George Bush in 1988 played an important role in his defeat, said he has learned one particularly important lesson after participating in hundreds of debates - including 39 against Gore during the 1988 Democratic primaries.
That lesson, Dukakis said, is to focus more on selling yourself than on trying to sell the detail of every policy.
''I am the last guy in the world to give advice to presidential candidate,'' Dukakis said. ''But you want to come out of there sounding and looking like you belong in the job. Draw a very clear contrast of what you stand for and the other guy stands for, but give people a real sense of who you are.''
John Aloysius Farrell of the Globe Staff contributed to this report.
