A powerful member of Congress and a big-time Republican contributor lined up behind one candidate. A Byrd machine delegate came out of political retirement to promote another. Fairfax Republicans pushed one of their own.

All were drawn by perhaps the most valuable piece of patronage Republican Gov. John N. Dalton can bestow on a Northern Virginian -- a seat on the state highway commission that dispenses $750 million a year in road contracts. Whoever wins the seat will have what other commissioners say is the virtually unquestioned ability to say where highways should go in the Washington suburbs.

The post became available on a Friday last month, when William B. Wrench resigned because of conflict-of-interest allegations. By Sunday the maneuvering in the secret campaign had begun in earnest.

In the month since that September weekend, the politicking has centered on inter-county rivalries, gubernatorial politics, Dalton's anger at Fairfax County's top Republican officeholder, feuding among the Fairfax supervisors and access to the GOP's money men who in turn have access to the governor. Yet for all the lobbying, no winner has emerged.

By last week the jockeying seemingly had produced a clear frontrunner -- a stockbroker from Woodbridge with all the right credentials -- and in the normal course of events he would have been named on Thursday.

But before the press release could be typed, a second highway commissioner had been forced out of office on conflict-of-interest allegations, a blow unprecedented in the commission's history. Dalton, mindful of the potential damage a questionable appointment could do to Republican gubernatorial candidate J. Marshall Coleman, derailed the stockbroker's nomination on grounds of potential conflict of interest and returned the issue "to square one," a Dalton spokesman said.

One of Dalton's principal concerns all along had been to limit the political damage to Coleman, who had to oust Wrench from his finance committee when the conflict-of-interest charges surfaced. At a closed-door breakfast meeting with Virginia's Republican congressmen at the Hyatt Regency hotel on Capitol Hill last week, Dalton said he believed the Wrench affair had seriously hurt the Republican campaign in populous Fairfax -- where GOP strategists believe Coleman must do well to win.

"I think the governor would like the highway commission to disappear until after the election," one participant at the breakfast said later.

Dalton was reportedly furious at the Democratic-controlled Fairfax Board of Supervisors and its Republican Chairman John F. Herrity for harming Coleman by keeping the Springfield Bypass controversy alive. It was a commission vote approving the bypass, a proposed $200 million highway through Fairfax, that forced Wrench to resign after The Washington Post disclosed that he owns land along its route.

"Somebody else said the Springfield Bypass is like an octopus dragging everybody down," the same participant recalled. "And the governor said, 'Yes, with a lot of help from certain people.' "

Herrity, who talked by telephone with Dalton for more than an hour to try to smooth things over last week, said at most there was "some breakdown in communications."

Prince William Republicans had sensed an opening. Their county is in the same highway district as Fairfax, and with its rapid growth rate it has comparable road problems -- including the question of how to funnel thousands of Washington-bound commuters through Fairfax.

"I said, 'Wouldn't it be great if we could get that seat?' " recalls Eileen Barnes, a Prince William GOP supervisor who was attending an unrelated political strategy session the Sunday after Wrench resigned. Someone suggested Andrew J. Donnelly, a Washington stockbroker and a former supervisor, who said he wouldn't object, and the campaign began.

One of Donnelly's key supporters was John D. Marsh of Gainesville, a retired millionaire who donated $8,000 to Dalton's gubernatorial campaign in 1977 and $5,050 to Coleman's. Another was Rep. Stanford Parris, the Republican member of Congress from Fairfax and Prince William who had hoped Donnelly's appointment would help him in an area where he is weak.

Republicans from Washington's inner suburbs, which have owned the seat for the last 20 years, warned of political fallout. "We've told the governor it would be a cause of great disappointment on the part of Northern Virginia Republicans if the seat were transferred," said Alexandria Sen. Wiley F. Mitchell Jr.

Mitchell and other GOP legislators support Fairfax Supervisor Marie Travesky, who says she is willing to serve. Travesky, who shares party label but little else with Herrity, says she doesn't believe Dalton's annoyance with Fairfax will affect her chances. "I think he knows what's going on up here well enough to know that Jack is Jack and me is me."

Dalton spokesman Charles J. Davis said the governor was "shaken" when he unexpectedly had to oust the second commissioner. The governor then reevaluated Donnelly's nomination with more attention to conflict-of-interest laws.

Donnelly's firm sells bonds for the highway commission, and the governor eventually told Donnelly that would have to stop if he were appointed. "It's a source of pride, and we wouldn't even consider giving it up," Donnelly said.

Conflict of interest questions also knocked out Giles Miller, a septuagenarian stockbroker from Culpeper. Miller was supported by D. French Slaughter Jr., a Byrd and Dalton supporter and former state legislator.

John T. (Til) Hazel, a major Dalton supporter who was influential in recommending Wrench, said this time the process had turned into a political nightmare. "I wouldn't touch it with a million-foot pole," he said.