RICHMOND, NOV. 10 -- Former Virginia governor Charles S. Robb announced today that he will seek the U.S. Senate seat being vacated by Republican Sen. Paul S. Trible Jr. and ruled out accepting a spot on the national Democratic ticket next year.

Robb, one of the new breed of fiscally conservative Democrats with wide appeal to centrist Republicans, is credited with rebuilding his party in Virginia to the point that it now holds the state's top three elected offices. The Democratic nomination is considered his for the asking and no Republican in sight is given much chance in early polling.

Robb said he wants to help return the national party to the mainstream because in recent years it has "too often strayed from its historic mission." He said he would not endorse a candidate for president until after the March 8 Super Tuesday primary, but would concentrate on "moving the message and the dialogue into the mainstream."

Robb, 48, served as governor from 1982 to 1986; under Virginia law he could not succeed himself. He is often mentioned as a vice presidential or even presidential nominee and despite his disavowal of national ambition, his announcement speech today sounded more like that of a candidate for president than for the Senate.

"It's time once again for Virginia to lead this nation, in defining the challenges of a new political and economic era, to renew America's promise of equal and expanding opportunity, to rededicate ourselves to the defense of liberty and the advancement of human rights and social justice at home and abroad," he said.

His prepared text was so cosmic that Rep. Stan Parris (R-Va.) said he thought Robb might have left "a crack in the door" to be drafted for the national ticket, but Robb pledged in response to a reporter's question that he will "not accept any nomination or appointment in the executive branch" next year. He did not rule out seeking national office in 1992.

"I'll keep my options open," he said. "I'm not gratuitously burning bridges, although I have no hidden agenda, no current intentions. Often the best way to get things done is not to declare yourself politically dead."

Trible, a freshman, surprised and angered his party when he announced Sept. 19 that he would not seek reelection. Trible cited family reasons, but some speculated he was leaving because early polls showed that he would lose in a matchup with Robb.

Yesterday a veteran Republican congressional aide said of Robb, "I don't know anyone who has a realistic chance of beating him" and said that no members of the state's delegation to Capitol Hill would risk giving up a seat to challenge Robb.

A poll conducted three weeks ago by the Richmond Times-Disptach showed Robb handily beating any GOP nominee. Former state attorney general J. Marshall Coleman, whom Robb defeated for governor in 1981, fared best, trailing Robb 61.8 percent to 18.3 percent; next came former secretary of state Alexander M. Haig Jr. of McLean, who trailed Robb 65.1 percent to 16.1 percent.

When matched against former Navy secretary John F. Lehman Jr. of McLean and Republican U.S. Reps. Parris, Frank R. Wolf, Thomas Bliley Jr. and Herbert Bateman, Robb was favored by about 6 to 1. Against television evangelist Marion G. (Pat) Robertson of Virginia Beach, who is sometimes mentioned for the Republican nomination, Robb was leading 77.1 percent to 8.2 percent. The poll did not list Marine Lt. Col. Oliver L. North of Great Falls and Iran-contra fame, also sometimes mentioned as a possible Republican nominee.

Robb has been a Washington partner of the Richmond-based law firm of Hunton and Williams since leaving the governor's mansion. He made his announcement today in a conference room at the firm's headquarters here before a cluster of former gubernatorial aides and current law partners, then answered questions on topics ranging from his personal life to foreign and domestic matters.

When asked about reports earlier this year that a Norfolk federal grand jury was looking into allegations he had attended parties at which cocaine had been used, Robb said, "The bottom line was that there simply was nothing there. I have never even seen any illegal drugs at any point in my life."

Robb, who served 13 months in Vietnam as a Marine combat officer, said, however, that "had I been born a few years later, I might well have been tempted. But I have never even been exposed to that temptation."

Robb said he has been "very fortunate" to have had "a strong and stable marriage" for 20 years, during which "the only person I have loved, emotionally or physically, is my bride, though, like any other red-blooded American, I have some fun from time to time, but I don't think that's either disqualifying or inappropriate."

He joked that "a couple of times I have been a little heavy on the . . . gas pedal," and that in the 1950s he received a traffic ticket, "though I can't say that's the only time I ever sped. And on a couple occasions I have made a small wager on the golf course. Otherwise, I have not knowingly broken any laws," he said.

"I'm more human, and a little less stodgy, than my reputation is sometime reported."

As to whether such questions are proper, he said, "if you want real people involved in public life, you have to make a judgment as to what's relevant. That is not to suggest that the pendulum has swung too far." He said he thinks the news media have "held the line on voyeurism reasonably."

On current issues, Robb said he would:Likely have come to the same conclusion as Virginia's senior senator, Republican John W. Warner, and voted against the confirmation of rejected Supreme Court nominee Robert Bork. Support research and development money for the Strategic Defense Initiative (Star Wars) but wants to make sure it could fulfill its mission before funding deployment for atmospheric testing. Balance the budget by employing a three-part solution. He would reduce domestic spending by putting "everything, and I mean everything" on the table for reexamination, including establishing a means test for basic entitlement benefits such as Social Security; cut defense spending by reducing procurement costs -- "not just on coffee pots and toilet seats" but by eliminating duplication among the services -- and finally "if you can't solve it on the expense side, by looking at the revenue side," which means raising taxes.

It was only 10 years ago that Robb made his first appearance as a politician. At the time, his claim to fame was that, as a Marine guard assigned to the White House, he had wooed and won the eldest daughter of President Lyndon B. Johnson, Lynda Bird. After a 1967 White House wedding, Robb went to Vietnam, where he won a Bronze Star.

When he returned, Robb enrolled at the University of Virginia law school. After graduation and a stint as a lawyer, and with the help of money from national Democrats and cronies of his late father-in-law, he won a three-way race for the Democratic lieutenant governor nomination. Then Robb got 54 percent of the vote in defeating GOP state Sen. A. Joseph Canada Jr. of Virginia Beach and was the only statewide Democratic winner. Republican John Dalton became governor.

Four years later, Robb beat then-Attorney General Coleman for governor, ending a 12-year Republican run in the statehouse.

Even before he left the governor's office early last year, Robb was mentioned as a possible candidate for the Senate, but he appeared reluctant to commit himself and talked of not wanting to be a legislator. He remained politically active and highly visible, helping found the centrist Democratic Leadership Council and making frequent speaking appearances.

Some contended Robb was holding out for lightning to strike in next summer's Democratic National Convention. He even encouraged Ronald I. Dozoretz, a wealthy Virginia Beach psychiatrist, to challenge Trible. But Dozoretz's bid never got off the ground, and he stepped aside in September, just five days before Trible's withdrawal.

Trible said in a statement that "Chuck Robb will be a strong contender. However, the Republican Party is vigorous, and will field a well-qualified candidate." He predicted "1988 will be a great Republican year. Our presidential candidate will win Virginia decisively, and Virginians identify with the Republican philosophy of national government."

Others, starting with Warner, were less optimistic. Warner said that "although Gov. Robb is a highly credible, competent candidate, the Republican Party has an obligation to come forward with its own strong candidate. In the interest of preserving Virginia's two-party system, Virginians must be given a choice."

Choice or not, Warner is prepared to work with Robb, saying, "This is a critical period in America's economy and national defense, and I pledge to form a close working partnership with whomever Virginians send to the Senate in 1988."