Jack E. Robinson, a 39-year-old businessman with such a checkered past that he was disowned by his own party's leaders, said he would appeal the ruling by the State Ballot Law Commission.

If the appeal fails, it will be the first time since 1916, the year U.S. senators were first popularly elected, that a Massachusetts Democratic Senate candidate has had no Republican opponent. The deadline for filing nominating papers was May 9.

The commission scrutinized 10,139 certified signatures submitted by Robinson and knocked off 153 signatures, putting him below the minimum needed to get his name onto the September primary ballot.

The commission also referred its findings to the state attorney general to look into "false and fraudulent signatures" that were particularly prevalent in four communities."

"It appears criminal violations of state election laws may have occurred," the commission said.

Robinson said Friday that he knows nothing about false or fraudulent signatures but will cooperate with any criminal investigation. He said he hired professional signature-gatherers.

"It's unfortunate we are going to have to spend the summer fighting legal issues," he said. "We are confident that the Supreme Judicial Court will give us our 14 signatures back."

Robinson also said that more than 100 other signatures that had been dismissed by Secretary of State William Galvin before the commission's investigation should be ruled valid. Galvin said the signatures were invalid because portions of the signature sheets were printed upside down.

Robinson was expected to have little chance anyway against Kennedy, who also also faces a Libertarian Party candidate.

"Senator Kennedy is looking forward to the re-election campaign regardless of his opponent," Kennedy spokesman Will Keyser said.

John Brockelmen, the executive director of the state Republican Party, declined to comment.

Both the Democratic and Libertarian parties had challenged the validity of Robinson's signatures.

Robinson was welcomed initially as a candidate bold enough to take on Kennedy.

But he quickly ran into trouble. The state's top Republicans, including Gov. Paul Cellucci, withdrew their support after embarrassing details of his past were revealed, including his arrest on charges of drunken driving, of which he was eventually cleared, and the existence of a restraining order taken out against him by a former girlfriend.