Republican senatorial nominee Richard D. Obenshain, at once the architect and the product of a resurgence of political conservatism in Virginia, died Wednesday night in a fiery light plane crash in suburban Richmond.

The articulate, bespectacled lawyer - a former cochairman of the Republican National Committee and Virginia's former state GOP chairman - was returning home from a campaign appearance in Winchester when his plane crashed and burned in thick woods a quarter mile short of Chesterfield County Airport.

Killed with him were two pilots, identified as Richard F. Neel of Alexandria and Ronald Allen Edenlen of Camp Springs, in Prince George's County. Investigators said they were unable to say which man was at the controls when the plane crashed.

Federal Aviation Administration officials said the plane had been in contact with flight control at Richmond's Byrd Field, gave no indication of trouble, and had reported the Chesterfield runway in sight shortly before the 11:10 p.m. crash.

Witnesses near the field, however, said the twin-engine plane appeared to be very low on its approach to the airport's single 4,400-foot-long runway, southwest of Richmond. Investigators said yesterday they could not cite a cause for the crash, news of which stunned Democratic and Republican officials.

Obenshain, 42, was opposing Democrat Andrew P. Miller, a former state attorney general, in the Nov. 7 election for the Senate seat being vacated by Republican Sen. William L. Scott.

Republican state Chairman George McMath said he would announce Monday when and where the party's 78-member State Central Committee would meet to choose a new candidate.

"He was . . . a courageous spokesman for the principles in which he believed . . ." McMath said. "He was a deeply committed man and the tragic accident . . . deprives America of the kind of leadership it sorely needs. His passing is a terrible blow to Virginia and the nation."

Miller said he was suspending all campaign activities for the immediate future because of Obenshain's death.

"Although Dick and I had our differences, I greatly respected him," the Democrat said. "He was a gallant fighter for the causes be believed in."

A serious, single-minded conservative from his earliest college years, Obenshain devoted much of his life to transformation the state GOP from a token opposition movement to the dominant political force in the commonwealth.

When he started, in the heyday of the old Byrd Democratic organization, Republicans held only two of Virginia's 10 House of Representatives seats and had not elected a governor or U.S. senator since Reconstruction.

Now, the GOP holds six House seats and the Democrats have not won an election for governor or the Senate in nearly 12 years.

"His brilliant leadership in directing the Virginia Republican Party to political dominance . . . was one of the outstanding political successes in the nation," said former Sen. William Brock of Tennessee, chairman of the GOP National Committee.

"His determination, dedication and leadership, combined with human traits of decency, kindness and . . . fair play cannot be replaced . . ."

Obenshain's efforts were built on a combination of ideology and organization. He often insisted strongly that the large majority of Virginians were politically conservative as he was himself.

But most of them, he said, were unwelcome among the conservative Democrats who ruled Virginia during the second third of the 20th century.

In the summer of 1964, when Obenshain first campaigned for public office, the political structure that had dominated Virginia for more than 30 years showed every sign of coming apart.

U.S. Sen. Harry Byrd Sr., the long-time patriarch, was old and sick. The state's Democratic Party had handed Byrd a rebuke by endorsing, over his objection, the reelection of President Lyndon B. Johnson.

The state's poll tax, which had restricted black participation in Virginia elections for more than half a century, had just been struck down by the federal courts and blacks were registering to vote by the thousands. The state seemed destined for a future in the mainstream of national Democratic politics.

But Obsenshain recognized that something else was happening in Virginia - something far less obvious. New people were moving into the state - many of them drawn by state campaign of industrial development under way since 1961.

In the tradition-minded Virginia of Harry Byrd, most of the new Virginians became political and social outsiders - middle management executives and white-collar workers who settled into the fast-expanding suburbs of the state's metropolitan areas.

Harry Byrd Sr. neither liked nor understood metropolitan areas, much less suburbs. His Virginia was a rural, agrarian state wedded not only to old principles but to old families, old blood lines and old loyalties. New People were looked on with suspicion.

In 1964, no better example of this phenomenon existed than in Viriginia's 3rd Congressional District - Richmond and its two surrounding suburban counties of Henrico and Chesterfield.

There, in the time-honored Byrd tradition of anointed succession. Democrat David E. Satterfield III was running for a congressional seat that had once been held by his father, an old Byrd ally.

The Republicans nominated Obenshain, then 27, an agronomy professor's son from Blacksburg by way of Bridgewater College and New York University Law School. He was almost totally unknown.

But in the 3rd District - most conservative of Virginia's 10 House districts - he had a weapon. He ran far to the right of Satterfield - himself an ultraconservative. Throughout the district huge billboards showed the boysih GOP candidate shaking hand's with the party's controversial presidential nominee, Sen. Barry Goldwater of Arizonna.

"GOLDWATER," the signs read, "NEEDS OBENSHAIN!"

When the votes were in Obenshain had lost by only 654, despite a conservative split in a three-way race. For the Republicans he was man to watch.

Obeshain and the Republicans had identified a new electorate in the state and exploded it with conservative appeals. Suburban housewives, management trainees and conservative college students turned out to organize burgeoning precincts ingnored in past elections by rural-oriented conservative Democrats.

Once strong only in the mountains and the valleys of Virginia's South-west, the state GOP had found a home in the suburbs.

Obenshain and Virginia conservatives, however, remained a minority wing of the state party. The major machinery was controlled by moderates like Linwood Holton who envisioned a GOP focused less on ideology than on broad-based problem solving appeals.

Obenshain fought for and won a place on Holton's statewide ticket in 1969, and though he lost to Miller in the race for attorney general (in a campaign that earned him the nickname "Nightstick Dick" for his get-tough stand toward college demonstrators) the GOP with Holton won its first Virginia governorship in this century.

That campaign proved the beginning of the end both for Virginia Democrats and for Holton and most other moderates in the GOP.

Spurred by a bitter Democratic primary fight and appeals from both Holton and Obenshain, a hard-core organization of wealthy conservative Democratic businessman publicly switched parties, declaring that the only hope for Virginia conservatives lay within Republican ranks.

Three years later, with the aid of those new allies, Obenshain became state Republican chairman, wresting control of the party from Holton and the moderaes. That year, with the help of Obenshain, Rep. William L. Scott won the first U.S. Senate election of any Virginia Republican in this century. The following year Obenshain was instrumental in persuading former Gov. Mills E. Godwin Jr. to leave the Democratic Party and win reelection as a Republican. This year, Obenshain was running for the Senate on his own.

Through it all, Obenshain never lost his belief that a return to limited government, individual initative and a free enterprise economy was as much a philosophical crusade as a political movement.

Throughout his Senate campaign he had stumped for the Roth-Kemp tax cut bill, calling for a 33 per cent reduction of federal income taxes as a weapon against big government.

"We can build our Republican majority into a permanent Republican landslide," he said, "by attracting those voters who base their political allegiance on the bread and butter issues that affect their families' welfare."

Democratic Del. Lewis Fickett of Fredericksburg, who shared the platform with Obenshain during the candidate's last appearance in Winchester, said "the essence of the speech was the necessity of individual freedom and the vitality of private initiative which are the cornerstones of American democracy." Fickett called it "one of the most moving speeches I've ever heard."

Sometimes tough-talking and usually serious in his speeches, Obenshain was rarely personal in his charges and had an unusual reputation for both hard politicking and fairness, as well as candor in his dealins.

Though Miller was considered an early favorite in the Senate race, Obenshain had made impressive headway particularly in financing, and had backed Miller in last year's governor's race.

"I just reflect on the long time we've worked together and the magnificent contributions he's made," said Holton. "Now here he was on the verge of tremendous success . . . "

Obenshain is survived by his wife, Helen, and three children, Mark, 15; Anne Scott, 13, and Kate, 9.

A funeral service will be held at 10 a.m. Saturday at Second Presbyterian Church in Richmond, with burial at 4 p.m. at Mill Creek Baptist Church in Botetourt County, adjoining the Obenshain family home.