After a four-year exile, the Virginia Senate's Old Guard leaders are on the verge of recapturing most of the powers they lost in a coup engineering by Northern Virginians.

Having stripped the Washington suburbs of a major leadership position before the session began, the conservatives are expected to consolidate their gains this week, restoring important taxing powers to the Senate's crusty senior member.

A curious coalition of moderates and liberals has joined with the conservatives to boost the role of Edward E. Willey, 69, the man who ruled the body for years with an firm, unrelenting grip.

His reemergence as a major power has troubled some liberals who recall the years he directed the Senate's affairs with the air of a Virginia patriarch and his distaste for much of the legislation that Northern Virginians sought.

Willey's supporters have said they have more than enough votes to restore to Willey's Finance Committee the power to rule on local tax measures, a prerogative that was stripped from Willey four years ago.

"It means that anybody who wants authority for any little tax bill will have to go hat in hand to Ed Willey," says state Sen. Joseph V. Gartlan (D-Fairfax).

For Willey, the action expected Thursday will cap a week in which he has reemerged as a major force in state government. Besides the restoration of his committee's authority, Willey has been a key figure in the continuing controversy over Gov. John N. Dalton's gasoline sales tax proposal.

On Monday, Willey bluntly told the governor behind closed doors what many other legislators had been saying to each other: that Dalton's proposal to tax wholesale gasoline prices by 4 percent had no chance of passage. When word of Willey's message leaked out, even Dalton's closest advisers admitted the proposal was dead.

It was then that Willey and three other Democratic assembly leaders, Senate Majority Leader Hunter B. Andrews, House Speaker A. L. Philpott and House Majority Leader Thomas W. Moss Jr., took control of the tax issue. They met with Dalton yesterday afternoon, scolded him for inept handling of the tax proposal, and suggested that Dalton revise his proposal and present it personally to the assembly.

The governor agreed. In a dramatic gesture designed to impress the lawmakers, Dalton scheduled an appearance this Friday before a joint meeting of the House and Senate finance committees -- a meeting that Willey will co-chair.

At that time, Dalton is expected to announce abandonment of the 4 percent tax approach and propose instead a 4-cent-a-gallon tax to be used for highway and Metro construction. The legislative leadership believes such a proposal, which may be whittled down to 3 or even 2 cents per gallon, has a much better chance of passing the tax increase-wary assembly.

Dalton also has taken the Democrats' advice in selecting the chief patron for the tax bill -- De. Vincent F. Callahan Jr. of Fairfax, chairman of the assembly's joint Republican caucus.

Some Republicans admitted they were embarrassed that their party's leader, who had campaigned energetically against Democrats last fall was now relying so heavily on Willey and other Democrats while leaving many Republicans in the dark about his plans. Several Democrats boasted that Dalton had miscalculated so badly that only the Democratic leadership could salvage some sort of tax bill.

"He's having to turn to the very people he dumped all over during the election," said Del. Warren G. Stambaugh (D-Arlington).

Whatever the results, one of the winners in this legislative chess game clearly will be Willey. Close colleagues say it is a sweet triumph for the white-haired Richmond Democrat after four years on the edge of legislative leadership.

Originally a product of the old Byrd organization, Willey made his reputation over the years as an archconservative in the Virginia tradition of tightfisted government. He has always been considered hostile to the many of the goals and legislation pushed by Northern Virginians and has been an ardent foe in the past of state funding of Metro.

A confidant of both Dalton and his immediate predecessor, Mills E. Godwin, Willey is a retired pharmacist who spends each work day operating out of a small two-room office on the first floor of the Capitol. As a 28-year veteran, he is said to have extensive knowledge of the budgets of various state agencies and as Senate finance chairman, he has had virtual life-and-death authority over their funding.

Friends say Willey was shocked and deeply hurt in 1976 when Sen. Adelard L. Brault (D-Fairfax) and a coalition of moderate and liberal Democrats succeeded in ousting him from the chairmanship of the then-powerful Senate Rules Committee. It was one of several changes that thrust the balance of senatorial power from the Old Guard to the coalition. As part of the triumph, Brault became majority leader.

Willey, Andrews and several other allies who fell from power bided their time, cemented friendships with some of the Senate's new members and waited for an opportunity to do unto Brault what they felt Brault had done unto them.

They go their chance last month.

The group that Andrews put together included some of the Senate's most liberal members, among them L. Douglas Wilder (D-Richmond), the Senate's only black member. Wilder says his decision to join Andrews and Willey was based more on "practicalities" than on philosophical agreement. Wilder says he has no problem working with "colleague Willey, even though Willey has been known for making racist remarks in private.

"Ed Willey's come a long way," says Wilder. "He was instrumental in getting James Sheffield [a local black judge] onto the circuit court here and he's gotten money for a sickle cell anemia program. We understand each other and I think we have a genuine fondness."

Willey himself is quick to deny publicly that he is back in control.

"Don't believe what you read," he said today. "I've never had any power down here and I don't have any now and you can't lose or get back what you never had."

But sometimes Willey is less reticent. While presiding over a Finance Committee meeting recently, he became curt with highway department officials while quizzing them on the gasoline tax proposal's stipulation that some revenues go to Metro.

"I don't see any couple of million in there to help us," said Willey, referring to Richmond's costs for its Downtown expressway and three toll bridges. "Since you're giving $27 million to Metro rail, did you all give some consideration to our request?"

When a department officiaal sheepishly replied in the negative, Willey straightened up in his chair and announced: "Well, I'm telling you now that you're going to."

At times the strong-arm approach has backfired. At a recent meeting of the state Community Colleges Board, Willey spoke in favor of a new college campus site in rural Goochland County. He warned the board that it would be politically unwise not to go along with him.

The board members took offense at Willey's comments and voted down the new campus. Later some members admitted that the proposal would have passed had Willey kept his mouth shut.