Former Virginia governor Charles S. Robb kicked off his Democratic campaign for the U.S. Senate last night with a black-tie fund-raiser that brought in more than $1 million, making it the most profitable political event in state history.

About 515 people paid $2,000 apiece -- the maximum personal contribution allowed by federal law -- to sip cocktails and dine with Robb at a Tysons Corner hotel, and in the course of the evening contributed almost 25 percent of Robb's anticipated campaign budget.

Organizers of the event said that after all the checks are counted and the bills are paid, they will clear about $950,000.

According to several state political activists, no previous affair in Virginia -- including a 1985 Republican luncheon whose featured guest was President Reagan -- has grossed more than $600,000. Several national fund-raising experts said that even for presidential candidates, million-dollar parties are rare.

Robb's chief fund-raisers hoped the occasion would send a message to Robb's potential Republican opponents and to Democrats outside Virginia who are looking for future presidential timber.

"This ought to send a little signal across the Potomac, shouldn't it?" asked Del. Alson H. Smith (D-Winchester), one of the organizers. "If we can do this now, just look at what we could do four years from now."

Robert Beckel, a prominent Democratic political consultant, said the occasion "gets five gold stars. It underscores the fact that Robb can attract a lot of money quickly, and that's a good sign for him in the long run."

The guest list for the event included notables from across the state and was particularly heavy with business and political leaders from Northern Virginia.

Several Northern Virginians who were cosponsors of the affair had previously contributed to outgoing Republican Sen. Paul S. Trible Jr., who announced in September that he would not seek reelection this coming November. The GOP has yet to find a Senate candidate.

Several of the Robb event's cosponsors have strong ties to well-known Republicans: Alexandria developer Myron P. (Mike) Erkiletian is a key fund-raiser for 8th District Rep. Stan Parris; John M. Toups, president of PRC Corp., raises money for gubernatorial candidate J. Marshall Coleman, and Fairfax developer John T. (Til) Hazel Jr. supported former Fairfax County Board chairman John F. Herrity.

"We've intentionally gone out and sought a broad base of people," said William G. Thomas, an Alexandria lawyer and key Robb adviser. "The Republicans may have to go out and find new sources of money {for their Senate campaign}. Raising money against Chuck will be tough."

Larry J. Sabato, a political scientist at the University of Virginia, said the event demonstrates the fund-raising prowess of Robb's organization, in particular Smith and Thomas, who have long been considered among the most formidable financial teams in the state.

"Only Chuck Robb and his people could turn out a crowd like this in Virginia," Sabato said.

Sabato and the fund-raisers said it reflects an important trend in Virginia politics: the declining influence of Richmond's insular and conservative "Main Street" business community, which virtually controlled the state's political purse strings until the early 1980s.

During this decade, the booming Tidewater and Northern Virginia regions have become rich sources of contributions.

The economy of these two areas "has grown, and the people there have become more civic-minded," Thomas said. "Northern Virginia, in particular, draws on the strength of the entire Washington area. People who might be considered Maryland-oriented or D.C.-oriented participate {in Virginia politics}. They've got business interests here."

Robb said he was "assuming there will be a strong, credible opponent" fielded by the GOP and that "this will put us off to a good start." He added, "you appreciate your friends."