Paul S. Trible Jr., whose decision to quit the U.S. Senate next year has left Virginia Republicans desperately seeking a possible successor, has transformed himself overnight into the man to beat for his party's nomination for governor in 1989, according to state GOP leaders and Trible associates.

In a series of shrewd strokes over the past week, including financial contributions to a host of Republican legislators and culminating Saturday night in a televised promise "to make a difference in the life of our state," Trible jumped in front of the field of politicians hoping to lead the GOP's state ticket in two years.

Political observers around Virginia said in interviews during the weekend that Trible would be a formidable candidate in his party -- where few enjoy his statewide name recognition and considerable financial resources -- and, more important, against Lt. Gov. L. Douglas Wilder or state Attorney General Mary Sue Terry, who are likely Democratic contenders.

So high is the partisan fever about a Trible candidacy in 1989 -- a sentiment tempered by fears that the Democrats will win his Senate seat next year -- that senior Republicans expect Trible to stop just short of announcing for his party's nomination at a news conference he is scheduled to hold in Richmond today.

"People may interpret what he says as more of a 'Go' than a 'No'," one Trible confidant said yesterday.

Other Republicans were more emphatic. "The idea that Paul would disappear and just become a corporate lawyer and make a lot of money is not a likely scenario," said Edward S. DeBolt, an Alexandria pollster who managed Trible's media campaign for his 1982 Senate election.

"The guy's a scrapper," DeBolt added. "He's a steely, intense politician."

Indeed, as sincere as Trible may have sounded when he said he was retiring to spend more time with his family and escape the workaday drudgery of a senator's life, the 40-year-old former prosecutor and House member remains just as ambitious as he ever was, according to several of his political allies.

Other observers said that far from being an aberration, Trible's surprise announcement was the latest in a long line of high-risk gambits to win public office -- while neatly sidestepping a confrontation with possible Senate candidate Charles S. Robb.

"It's one of the biggest riverboat gambles I've ever run across," said Larry Sabato, a University of Virginia government professor. "He gambled when he was 29 and was elected to the House. He gambled when he was 35 and was elected to the Senate. Now that he's 40, maybe it's time to gamble again."

Last week, even as he dropped the bombshell retirement news on a small circle of party elders, Trible raised the possibility of a gubernatorial campaign.

Virginia GOP Chairman Donald W. Huffman of Roanoke, in whom Trible confided a week ago, said he immediately asked Trible whether running for governor in 1989 would be inconsistent with his desire to see more of his family.

"He said, 'I don't think it would,' " Huffman recalled yesterday. "He said, 'If you're governor, your family lives there {next door to the state Capitol} with you. The governor can set his own agenda. A governor can decide to be home on a certain night and he's there. A senator can't."

In his televised announcement, Trible used almost the same words, saying, "I want to be better able to shape my day, set the agenda, do more for my family and for Virginia."

Former 2nd District representative G. William Whitehurst said he learned of Trible's intention when the senator telephoned Friday afternoon.

"I asked him, 'Paul, have you made any plans?' " Whitehurst said. "He said, 'I haven't, although there's going to be a lot of speculation about whether I'm going to run for governor.'

"I think his motivation {for not running again for Senate} is not running for governor," Whitehurst said. "But he ain't stupid."

However commanding Trible's position for the 1989 gubernatorial race may be, his decision to retire from the Senate marks an extraordinary setback for the Virginia GOP at a time when the party is attempting to rebound from the devastating statewide losses of 1985.

In opening the door to running for governor, Trible left his party without an obvious successor for the 1988 Senate race.

"After you get over the initial shock, this makes a lot of sense for Paul -- he's probably the strongest candidate for '89," said one party activist from Northern Virginia. But, he added, "It infuriates me as a party person because he's left the party a shambles for '88."

GOP Chairman Huffman noted, "We've lost not only two years of campaigning {for the Senate} but five years of service by an incumbent and $1.5 million in campaign funds," the amount Trible had raised in the past two years.

On the other hand, Trible's departure could help rejuvenate a state party that has had little to celebrate going into this fall's General Assembly elections. "Strangely, one of the things this has done is get people to say, 'Whoopee! This opens up opportunities for a lot of us,' " DeBolt said.

Noted Virginia GOP spokesman Steven Haner, "There are a lot of ambitious Republicans who spent sleepless nights Saturday."

Republicans groping for Trible's successor already have rounded up the usual suspects -- and added a few new names to the list of possible candidates.

Former state attorney general J. Marshall Coleman, who would like to be governor, and several Republican congressmen -- notably Reps. Stan Parris of Fairfax County and Tom Bliley of Richmond -- were mentioned in the wake of Trible's announcement.

In addition, former Navy secretary John F. Lehman Jr., current Navy Secretary Jim Webb, Army Secretary John O. Marsh, and presidential hopefuls Alexander Haig and Marion G. (Pat) Robertson -- Virginia residents all -- are being discussed as possibilities.

While Coleman and Parris have previously run for governor and have indicated they may run again, Trible's entry into the race would pose a serious threat to their chances. Not only does Trible already hold a statewide office, but also he would start with the powerful advantage of the $1.5 million war chest.

Experts familiar with federal campaign finance law said yesterday they are certain that Trible is entitled to transfer his Senate campaign money into a fund for a governor's race. Virginia's two major political parties expect their nominees to spend more than $5 million each in the 1989 campaign.

Huffman, while saying that the GOP has a number of good prospects, said Trible would make "a fine gubernatorial candidate. He's never lost a statewide race, and he's the only person we've got in that situation. He's got name recognition and the ability to raise money."

Sabato said, "There's a terrible vacuum at the top of the Republican Party. Nobody is satisfied with the choice of Coleman versus Parris. Trible will leave office undefeated, retiring gracefully. He will go out on a mountaintop."

There are signs that Trible is already using his campaign treasury to build goodwill among party regulars. Within the past week, according to party officials, an organization called Friends of Paul Trible sent $1,000 contributions to several GOP candidates for the state Senate and $500 donations to Republicans running for the state House of Delegates.

Meanwhile, the two Democrats most often mentioned as candidates for their party's gubernatorial nomination in 1989 offered differing appraisals of Trible's chances.

"Paul would make a fine candidate, like any number of other Republicans," said Terry, the attorney general. But, she added, "It's premature to speculate on the shape of either {party's} ticket."

Wilder, the lieutenant governor, said, "If I decide to run, I can beat anyone the Republicans put up." Staff writer Donald P. Baker contributed to this report.