Stumping in California, Gov. Michael S. Dukakis bragged Sunday about the liberal tradition, claiming that rival Vice-President George Bush was "dead wrong" in saying he wanted to divide the country. Bush, speaking in Philadelphia, shrugged off recent polls that showed his lead narrowing, saying he would campaign harder than ever in the final week before the Nov. 8 election

"I'm going to be a president who unites America," Dukakis told reporters during a day-long train trip through California's Central Valley. "If he wants to talk about that, then I'd be happy to meet him face-to-face."

Dukakis challenged his rival to a debate on election eve during the hour of network television time purchased by the Democratic and Republican campaigns for last-minute appeals to voters. A moderator would be present, but the candidates--not reporters--would ask the questions.

Bush said he did not think his support was waning in the final days of the campaign. Asked why the polls showed his once double-digit advantage over Dukakis appeared to be eroding, Bush replied, "I don't think they are, and I'm not going to say any more about it."

The GOP nominee spoke briefly to reporters outside the residence of Roman Catholic Cardinal John Krol, where he attended a private Mass with his wife, Barbara, and grandson George P. Bush.

Dukakis, convinced his campaign is surging in the waning days of the election contest, delivered an impassioned defense of liberalism, a subject he has largely ducked.

"We need a president in the tradition, yes, the liberal tradition, of Franklin Roosevelt and John Kennedy," Dukakis told a depot rally in Hanford, a valley community surrounded by sprawling cotton farms.

He repeated that call at similar rallies in Bakersfield and Fresno, adding former President Harry S. Truman to his list of liberal Democrats at those stops.

At the Fresno news conference, Dukakis said he decided "it was time to set the record straight" after President Reagan said last week that if Truman was alive today he would support Bush and the GOP.

Dukakis scoffed at Reagan's statement and said his fiscal conservatism and concern for children, health care, education, the environment and average families put him squarely in the mold of Roosevelt, Truman and Kennedy.

"That's the tradition of liberalism I grew up in," Dukakis said. "That's the tradition I believe in. And I'm not going to let the Republican Party pervert that word and give it a meaning it doesn't have."

In an interview with the "MacNeil-Lehrer Newshour," Dukakis said he objected to the manner in which Bush has used the term liberal to describe his opponent.

"A way which I think is very deliberately designed to suggest that I and people like me don't have a sense of values, that we're kind of permissive, that anything goes," he said in the interview taped Saturday and scheduled to air Monday night.

Yet at the Sunday news conference, Dukakis refused to add less popular liberals--George McGovern, Jimmy Carter and Walter Mondale--to his list.

"I'm not going to go through a litany of people" who share that tradition, Dukakis said when asked about the latter group of Democrats. He did, however, refer to a recent joint appearance with Carter.

Dukakis drew large and enthusiastic crowds at each of the depot rallies, taking time during each to speak in Spanish to the large number of Hispanics in the crowds.

As Dukakis adopted a more combative tone in his trip through California--he promised an administration with "more backbone" than the current one--his campaign also was fighting back with new ads attacking the Republican environmental record. One commericals shows two beachgoers wearing gas masks with an oil rig just offshore.

Recent public opinion polls show Dukakis closing fast on Bush in several key states including California, a must-win state where Dukakis aides said an 11-point Bush lead a week ago has shrunk to a virtual tie.

Nationwide, a Time magazine poll taken last week showed Bush maintaining a 10-point lead. But Dukakis aides said more recent tracking data showed the gap had narrowed to as little as six points.

Bush's chief of staff, Craig Fuller, said the campaign had expected all along to see a tightening in the numbers and was not alarmed by the latest apparent shift toward Dukakis.