Two of Virginia Democratic Gov. Charles S. Robb's closest political and financial backers joined today with the gubernatorial campaign of state Attorney General Gerald L. Baliles, who is scheduled to formally announce his candidacy for governor on Tuesday.

Lawyer William Thomas of Alexandria, a leading lobbyist in the state, and Del. Alston Smith of Winchester, a top Democratic fund-raiser, are among members of a statewide finance committee that will help raise money for Baliles, a Richmond lawyer who was elected attorney general in 1981 along with Robb as governor.

Under Virginia law, Robb cannot succeed himself.

The addition of Smith and Thomas was seen by many politicians as a long-expected flow of Robb's advisers to Baliles. The governor has said he will remain neutral in the contest between Baliles and Democratic Lt. Gov. Richard J. Davis of Portsmouth, who has announced for the office.

"I can't speak for the governor," Thomas said. "The press and the public have got to draw their own conclusions." Thomas said he expects to again concentrate on raising money in Northern Virginia.

Other Northern Virginians on the Baliles committee include former state senator Adelard L Brault of Fairfax, newspaper publisher Arthur W. Arundel of The Plains, Fairfax Democratic Finance Chairman Don Beyer Jr., Alexandria Commonwealth's Attorney John E. Kloch and Collister Johnson, Northern Virginia finance chairman for Robb in 1981.

George M. Stoddart, Robb's press secretary, reaffirmed Robb's neutrality today. "The governor has made it clear to all his friends and supporters that they should support who they are comfortable with. Many in the Tidewater area are already working and raising money for Dick Davis," Stoddart said.

Davis, a former Portsmouth mayor, is considered the frontrunner in the tight battle with Baliles. Davis has reported raising nearly $600,000, while Baliles has raised about $400,000.

Robert Watson, Davis's chief political adviser, said Davis is "very pleased with the progress of our campaign. We are very confident." Watson noted that several prominent Tidewater businessmen who raised money for Robb in 1981, including retailing executive Leonard Strelitz and psychiatrist Ronald I. Dozoretz, are now working for Davis.

Smith, chairman of the House Democratic caucus, has been instrumental in raising money for Patrick County Del. Mary Sue Terry, who is the only Democratic candidate so far for attorney general. "So far, the only thing I have agreed to do at this point is serve on the finance committee," Smith said. "I don't think fund-raising is such a serious matter until after the nomination."

The Democrats will select candidates for governor, lieutenant governor and attorney general June 7 at a state convention in Richmond. However, mass meetings will be held around the state in late March or early April to select convention delegates.

The effect is "140 local elections" rather than a statewide contest, said Curry Roberts, an adviser and fund-raiser for Baliles.