After more than a year of campaigning, it's down to nine weeks and a dead heat, with a volatile electorate that is as yet committed firmly to no one.

As the presidential race formally begins Monday with Labor Day kickoffs, Republican George Bush has made an unexpectedly strong comeback after months of trailing Democrat Michael Dukakis. Now both will be targeting the same groups of swing voters who have been dubbed the "persuadables," those who have not yet made up their minds or who still could be persuaded to change them.A private survey completed last week by Richard Wirthlin for the Republican National Committee showed an even race, a GOP source said, but also found that a stunning 47 percent of all voters indicated that they might change their mind or that they were uncommitted.

"I don't think these voters are that deeply anchored," Texas pollster Lance Tarrance said of the electorate. California pollster Mervin Field agreed: "Right now, it's up for grabs."

Actually, both candidates have more or less solidified their support among their parties' core voters. What remains important for Democrats about traditionally Democratic black voters, for instance, is the intensity of their support and the size of their turnout on Nov. 8.

Both candidates are now targeting - with every speech given and every television ad prepared - similar groups of swing voters who are largely politically independent or who identify only weakly with a party.

The major groups of swing voters and the issues expected to resonate with them are apparent: Blue-collar, ethnic Catholics in states like Ohio and Illinois who are worried about American competitiveness and their own jobs. White-collar baby boomers in California and elsewhere who are concerned about public education and the environment. Conservative whites, especially men, in Texas and other Southern states who care deeply about patriotism and the national defense. Working women in Pennsylvania and New Jersey and other states who feel hard-pressed about being able to provide adequate day care for their children and long-term health care for their parents.

Hispanics in Texas and California and politically independent white suburbanites in virtually every swing state also are among the keys to the election.

"If you've got an even race, in a sense it is all new, because it's not over for either guy," Republican strategist David Keene said. "There are a lot of people out there who haven't made a decision."

In fact, this is the first really close race at the Labor Day start since 1960. This year, the candidates' debates are expected to be critical, as they were then. One sign of the wide-open status of this year's race is that analysts can make the case for a photo finish or an electoral-vote blowout -- by either side.

Bush has staged his comeback from underdog status with a month of rough, tough, aggressive campaigning to which Dukakis has not yet effectively responded. Bush, according to pollsters, has peeled off some conservative white Southerners and Hispanics by portraying Dukakis as weak on defense and attacking his 1976 veto of a bill mandating teachers to lead the Pledge of Allegiance. He has made inroads among white suburbanites, Democratic pollster Peter Hart said, by vowing his own commitment to environment and education, whatever the record of the administration in which he serves.

"It has advanced more quickly than we had thought," Richard Bond, the political director of the Bush campaign, said happily. Hart agreed. "The difficulty for the Dukakis campaign is that they haven't been as aggressive as they should have been either, one, answering the charges that Bush has raised or, two, in making their case to the American public."

William Galston, a professor in the School of Public Affairs at the University of Maryland who has been active in national Democratic campaigns, likened the campaign generally to a football game.

"The game is played between the 40-yard lines," he said. "Roughly speaking, 40 percent of the people are precommitted to voting for the person who stands up and says, `Hi, I'm the Republican candidate for president,' and roughly 40 percent are committed to doing the same thing on the Democratic side. Then you have the 20 percent in the middle."

Those voters in the middle will be wooed with carefully calculated, daily campaign messages _ ousted Dukakis aide John Sasso was rehired Friday in large part for his skill at doing just that _ as well as sophisticated use of direct mail and telephone banks in swing precincts. (See news analysis on this page.)