RICHMOND, SEPT. 7 -- Gov. Gerald L. Baliles, barnstorming the state in a traditional Labor Day kickoff of the political season, gave a major boost today to a prospective U.S. Senate campaign by his predecessor, Charles S. Robb.

"We need Chuck Robb in the U.S. Senate -- and I am going to do everything I can to help him get there," Baliles told rallies in the western Virginia cities of Buena Vista, Covington and Waynesboro.

The endorsement was seen as the strongest signal yet of Robb's intention to run for the Senate next year against incumbent Paul S. Trible and to delay a possible presidential or vice presidential bid until at least 1992.

Trible, a freshman Republican who already has raised about $1.4 million for next year's reelection campaign, could not be reached for comment.

Baliles said he had sent a message to Robb about the planned endorsement. Robb did not ask him to announce his support, Baliles said, but he added that they had talked several times about his view that Robb should run. Robb is traveling in Africa and was unavailable for comment.

"We never discussed a specific time" for the endorsement, the governor said. "Otherwise I wouldn't have had to send him a message."

However, Chris Bridge, Baliles' press secretary, said, "I don't think Robb asked him not to" make the speech, which she called a "major step" toward a Robb candidacy.

Many Democrats say a Robb candidacy next year is the party's best shot in the foreseeable future at winning a seat in the Senate, where senior Republican John Warner is entrenched. The state's 10 House seats are evenly divided between Republicans and Democrats.

"All the polls show that a lot of people like the sound of 'Senator Robb,' " Baliles said. Recent surveys have given Robb a sizeable edge in a contest against Trible.

Del. Alson H. Smith Jr. (D-Winchester), the state party's premier fund-raiser, boasts that he could raise $1 million to $2 million for a Robb candidacy "overnight."

Robb may be the only challenger, other than multimillionaire Ronald I. Dozoretz, who could raise enough money to take on the well-financed Trible.

Dozoretz, a Virginia Beach psychiatrist, is expected to announce this week that he will not be a Senate candidate. Baliles said he talked to Dozoretz this weekend. "He has advised me he does not intend to be a candidate . . . that he supports Governor Robb for that seat, and will release a full statement later this week," Baliles said.

Baliles also stumped today for Democratic candidates for the General Assembly, where all 140 seats are on the ballot this November. But as he addressed relatively sparse small-town gatherings, the governor devoted his speeches to effusive praise of Robb.

He described Robb as "a candidate who knows how to balance a budget . . . who took Virginia schools forward when Washington was going in reverse . . . whose military leadership was tested in combat, whose political leadership was proven in executive office."

Robb has coyly avoided officially announcing his intentions for next year, a tactic that some backers say was aimed at holding the door open for a possible candidacy for president or vice president.

But even the recent decision of Robb's ideological favorite, Sen. Sam Nunn (D-Ga.), not to become a presidential candidate failed to nudge Robb toward dipping a toe into the crowded pool of would-be presidential nominees.

Nevertheless, Robb has worked hard at raising his visibility nationally as a leader of the Democratic Leadership Council and through speeches and travel around the globe. His confidants say those activities will help prepare him for a Senate race, as well as for a run at national office in 1992.