Virginia Lt. Gov. Richard J. Davis, dismissing claims that the state Democratic Party is in poor shape after its defeats in the November elections, yesterday became the first Democrat to announce formally for the 1985 gubernatorial contest.

Davis, 63, who narrowly lost a bid for the U.S. Senate in 1982, made announcements in Portsmouth, Richmond and Alexandria, portraying himself as a close ally and adviser to Democratic Gov. Charles S. Robb.

The former Portsmouth mayor, attorney and mortgage banker said, however, he has not asked for nor received the governor's endorsement. Robb, who under Virginia law cannot succeed himself, has said he will not take sides in the party's nominating process.

The governor publicly criticized Davis two years ago, saying that he lost his race to Republican Sen. Paul S. Trible, because he lacked "the fire in the belly" needed to propel a candidate into office.

Some Democrats still question whether Davis' campaign style is aggressive enough, but Davis said today that he always has wanted to be governor and that Robb believed that his desire for that office may have been so strong that it thwarted his bid for the Senate.

Davis also sought to shake the image that he is a liberal, saying that label is "unfair, unjust and untrue." He asked: "Have you ever seen a liberal mortgage banker?"

He recalled that when he ran for lieutenant governor in 1981, his opponent for the nomination, Ira M. Lechner of Arlington, accused him of being too conservative, and said there were anti-Davis campaign buttons that read "Save Us from Davis."

His announcement came a day after Democratic Del. Richard M. Bagley of Hampton, chairman of the House Appropriations Committee, announced he would not enter the race. State Attorney General Gerald L. Baliles of Richmond is expected to become a candidate for the Democratic nomination.

Davis, who has raised $567,000, is the acknowledged Democratic front-runner. He won the early endorsement of the Virginia AFL-CIO, and representatives of the AFL-CIO and the American Civil Liberties Union attended his kickoff in Richmond. Representatives of the NAACP were there, but said they were just observing.

Davis said he agreed that Virginia Democrats must attract more white, suburban males, who polls show are fleeing to the Republican Party. "But I still believe we should not, in our zeal to target that particular group, lose interest in" other groups that have traditionally remained Democrats.

"We want to broaden the base, but we do not want to do that in a substitution manner," said Davis, as applause erupted in the Alexandria City Council Chamber, where he made one of his three announcement speeches.

Davis declined to answer questions about the potential impact on the Democratic ticket of State Sen. L. Douglas Wilder of Richmond, a black who is the party's only announced candidate for lieutenant governor. Davis won the part-time job, which pays $20,000 a year, in a landslide over Republican state Sen. Nathan H. Miller in 1981.

Davis ran for the Senate after Wilder effectively blocked the candidacy of Del. Owen B. Pickett of Virginia Beach by threatening to run as an independent.

Davis' announcement yesterday was studded with references to fiscal conservatism, from a pledge to do "everything in my power to prevent the need for any tax increase," to a comment that " . . . we won't have any of the nonsense that goes on in Washington, spending more than you take in . . . ."

Davis, who is president and director of Virginia Investment & Mortgage Corporation, was Portsmouth mayor from 1974 to 1980. He was also chairman of the state Democratic Party in 1979 and 1980. During those two years, Democrats say he built a statewide following among party regulars.

"As its chairman, I helped rebuild the Democratic Party of Virginia -- a proud, important institution in Virginia's history, and a key to her future," said Davis yesterday.

He also said he "would do everything in my power" to avoid a tax increase, although he added, "It would be irresponsible to absolutely rule out any tax increase."

His other top priorities would be to encourage economic development, upgrade the state's transportation system, and improve the education system, said Davis.

"Today begins the culmination of my lifelong odyssey," said Davis, who said that as a young boy he sold peanuts to support his widowed mother.

He added, in one of his many references to Robb: "Like Lt. Gov. Robb before me, Lt. Gov. Dick Davis is ready, committed and determined to be your next governor."