Rep. Geraldine A. Ferraro, (D-N.Y.), as combative in her stump speeches and as witty with the news media as she has ever been, today wrapped up a weeklong swing up the West Coast by vowing "I'm in this fight" to the end.

With poll after poll indicating that her party's upset chances Nov. 6 are ebbing, the Democratic vice-presidential nominee increasingly cites precedents for dark-horse victories.

During a news conference early this morning, she invoked Harry S Truman's 1948 victory when, she said, "obviously the polls didn't mean a thing to the American people."

She also mentioned the upset victories of Texas Gov. Mark White, who she said trailed by 10 points in preelection polls, and Sen. Frank R. Lautenberg (D-N.J.), who she said trailed by 17 points two weeks before his 1982 victory.

Ferraro continues to insist that she and running mate Walter F. Mondale will profit from a massive turnout of women. In the next few days, the Democrats will unveil a television ad featuring Ferraro as a symbol of the aspirations and accomplishments of American women. The theme of the ad, Ferraro said, is: "We're proud of you, Gerry."

Ferraro said the Democrats have decided not to use an ad that would have featured footage from the first presidential debate Oct. 7 and indirectly highlighted questions about President Reagan's age and competence. There was concern that the ad would backfire by generating sympathy for Reagan.

After several days of appearing tired in public speeches and testy with the media, Ferraro returned to form on this West Coast trip, which was to end today with a return flight to New York via Waterloo, Iowa, and Detroit.

In a rally speech before a boisterous crowd of 10,000 here, Ferraro said, "They tell me there are people who are going to vote for Mr. Reagan even though they oppose his policies.

"Mr. Reagan may be charming, he may be funny, he may even be pleasant. But there is nothing charming about the covert war in Nicaragua, there is nothing funny about toxic-waste dumps that cause cancer, and there is nothing pleasant about discrimination against women and minorities."

At the close of her news conference this morning, Ferraro was asked about reports that press secretary Francis O'Brien jokingly was organizing a "guerrilla campaign" that would "take to the hills" in an unconventional hunt for electoral votes.

"If Francis is running for the hills," Ferraro replied dryly in her best deadpan, "it's because I'm going to be chasing him."