Virginia Lt. Gov. Richard J. Davis, hoping to keep alive his bid for the Democratic nomination for governor, said today he will challenge the credentials of as many as 750 delegates supporting state Attorney General Gerald L. Baliles, the party's apparent nominee.

Davis, 63, rejecting overtures that he give up the contest in the name of party unity, said it would show "a lack of commitment to my supporters" to concede to Baliles. The attorney general claimed victory last week after two days of delegate selection caucuses for the party's June 7 nominating convention in Richmond.

Baliles, with support from about 104 officially uncommitted delegates and about 50 state officials who are automatic delegates, has about 50 more votes than the 1,803 needed for nomination, according to his campaign. His staff expressed confidence today that it would beat back any threats to the nomination.

Meanwhile, in the contest for the Republican gubernatorial nomination, Rep. Stan Parris, who is competing with Wyatt Durrette, said he plans to continue his campaign at his party's convention in Norfolk, United Press International reported.

Durrette claims he has enough backing for the nomination, and a Durrette spokesman, Don Harrison, said, "Our assumption has been all along that Stan would stay in" the race for the nomination to succeed Democratic Gov. Charles S. Robb. "We had no reason to believe otherwise.

Parris campaign manager Jeff Gregson said, "The decision has been made that the Parris campaign is alive and well and moving forward. We believe that this thing is still winnable." He cited a new poll showing a growing number of Republicans worried about a possible rematch between Durrette and Baliles, who defeated Durrette for the attorney general post in 1981.

In Davis's race with Baliles, 159 of the Democratic delegates Davis's campaign is challenging are from Fairfax County, once seen as a Davis stronghold. Baliles scored victories there that were crucial in his apparent victory over Davis, who was considered the frontrunner in the race for the Democratic nomination.

The Davis campaign is challenging caucus results in four of Fairfax County's eight magisterial districts: Annandale, Springfield, Dranesville and Centreville. A spokesman said the challenges allege improper instructions from party leaders running the caucuses and dispute counting procedures in Centreville.

Davis said his campaign was not accusing Baliles of any improper conduct in the caucuses, but he declined to say whether his massive delegate challenge would involve charges as serious as gross incompetence by party officials and fraud.

For Davis to overturn Baliles his forces would have to strip Baliles of about 50 delegates through a complex series of party actions that would have to last through the convention. That would leave the Democrats divided going into the state's November elections, some party leaders say.

Davis appeared resolute and combative today at a State Capitol press conference and stressed his role in rebuilding the party in recent years. "I will not have my legacy be the man who built it and the man who destroyed it," he said.

Last week, both state Party Chairman Alan A. Diamonstein and Robb, who cannot succeed himself, appeared to signal to Davis that he should concede the campaign he has waged for more than a year.

The Baliles' campaign announced today it may also challenge some of Davis' delegates as well as the makeup of a temporary credentials committee, considered pro-Davis. The committee is scheduled to begin hearing challenges as early as next week.

Davis, a former mayor of Portsmouth, said today he has received an additional $140,000 from about a dozen Tidewater area businessmen. The new funds, including $50,000 from Virginia Beach developer R.G. Moore, puts Davis over the $1 million mark in fund-raising. Aides said nearly all of it has been spent. Davis also said he is cutting about 10 persons from his campaign staff of 25 now that the caucuses are over.

Chris Bridge, Baliles' campaign press secretary, said Baliles is going ahead with several party fund-raisers. She said the campaign has raised about $25,000 since the caucuses and has pledges of $100,000 more, which if collected also would put Baliles over the $1 million mark.

"We're doing it on our own schedule and not to react to him [Davis]," said Bridge.

Davis also announced that he had hired consultant Christopher J. Spanos of Fairfax to oversee the delegate challenges. Spanos, considered an expert on state party rules, is a Davis supporter and former administrative assistant to former representative Herbert Harris.