Former Virginia attorney general J. Marshall Coleman, in a move that reshaped the state's 1985 Republican gubernatorial campaign, announced yesterday that he has set aside his aspirations for the top spot to run instead for lieutenant governor.

Coleman's surprise action cleared the way for a two-way battle for the nomination between 8th District Rep. Stan Parris and former Fairfax delegate Wyatt B. Durrette. Both candidates immediately began scrambling to pick up Coleman supporters.

Coleman, who lost the 1981 gubernatorial race to Democrat Charles S. Robb by 110,000 votes, said his decision was reached over the weekend. While Coleman said he acted "in the interest of party harmony," his action was widely interpreted as a signal that Coleman felt he would have a tough time winning the nomination for governor.

During the recent months, Coleman has been actively assessing his chances, conducting polls, raising money and leading his party's criticism of the Robb administration's handling of prisons.

Coleman, 42, said he "sincerely felt" he could win the nomination and the governorship, but that he was concerned that the race might degenerate into a repeat of the acrimonious 1977 attorney general battle, in which he beat Durrette.

"People were anticipating another shoot-out at Dodge City," Coleman said, adding that the contest could have become "rancorous, protracted and expensive . . . . "

"I'm confident that this will be a net benefit to Durrette," said Donald W. Lemon, a law partner and political consultant to Durette, who has spent the past several years lining up support for his candidacy.

Parris, who announced his candidacy Nov. 21, said, "I'm not surprised by his Coleman's action, in the sense that, if his motivation was to be on the statewide ticket, this was his best chance."

Coleman's decision makes him the acknowledged front-runner for the number two spot. Party sources said none of the other hopefuls has statewide name recognition. The only announced Democratic candidate is state Sen. L. Douglas Wilder of Richmond, who is black. Three Democrats are seeking their party's nomination for governor: Lt. Gov. Richard J. Davis, Attorney General Gerald L. Baliles and Del. Richard M. Bagley of Hampton.

Coleman, who has practiced law in Washington since his defeat three years ago, said that he would not now endorse a gubernatorial candidate. Coleman has said privately he believes his decision will benefit Durrette.

That view is echoed by the Durrette camp and by many Republicans who say that, as the acknowledged front-runner, Durrette is in the best position to pick up Coleman delegates.

However, others say the bitter feelings between the Durrette and Coleman camps generated by the 1977 fight may aid Parris.

"It's a big development for the Parris-for-governor campaign. People for Marshall had been opposed to Wyatt," said Parris aide Dick Leggitt. "Now, as a logical progression, we will pick up the vast majority of those people."

Some party leaders suggested that Coleman's ability to raise money for a second try for governor would have been seriously hindered by his failure to repay $700,000 in campaign loans from the 1981 governor's race.

Coleman denied that he had left supporters in the lurch, saying that the lenders had agreed to turn the money into contributions. He said he has eliminated his campaign debt from 1981 and already has raised nearly $250,000, and has commitments for another $250,000 for his 1985 race.

Coleman, who served in the Virginia House of Delegates and state Senate, in 1977 was the first Republican elected Virginia attorney general in this century and the youngest person to hold that office. His fast rise led many to believe that he would have problems settling for the number two spot after coming so close to winning the top post.

However, while Coleman's polls showed that he had more statewide name recognition than either Durrette or Parris, Durrette has been the acknowledged favorite among party regulars, who will choose the nominee at a statewide convention May 31.

In addition, Republican sources said that the lieutenant governor's job, which is a part-time position, would allow Coleman to remain in the Washington law firm where he is currently earning a six-figure salary. Coleman moved to McLean in 1982 and is building a house there.

Coleman said he had discussed his decision with Durrette Sunday night. He said he could not reach Parris, but had spoken with him last week about the possibility that he would run for lieutenant governor. Both men told him he would be "compatible" as a running mate, although no promises were exchanged with either man, according to Coleman.