Undeterred by the wide lead of front-runner Andrew P. Miller, other candidates for the Democratic nomination to the U.S. Senate in Virginia vowed yesterday to stay in the race and support convention rules that would make an early ballot victory for any candidate unlikely.

Miller won about 1,000 first-ballot commitments from state convention delegates chosen Saturday. Campaign managers and candidates agree that he should get about 200 more first-ballot votes from uncommitted delegates, including elected officials who may be allowed to vote. However, this total of about 1,200 would leave him about 200 votes short of a majority and his opponents said they believe they can stop him there.

"Even if you call that the threshold to the nomination - and I don't - Miller wont't go beyond his first-ballot total," Sherman Webb, the campaign for candidate Rufus Phillips, said in an interview. "Someone is going to be nominated, but it won't be Andrew Miller."

State Sen. Clive L. DuVal II of Fairfax County finished second to Miller in committed delegates - 439 by his count - as a result of the city and county mass meetings on Saturday. He said at a press conference that he will pick up enough uncommitted delegates to go to the first ballot with at least 700 votes.

G. Conoly Phillips, the born-again Christian who brough out hundreds of evangelical supporters to the city and county meetings, claimed about 400 committed delegates yesterday and enough uncommitted to push his total to nearly 500.

They are followed by Rufus Phillips, a former Fairfax county supervisor, with 174 claimed committed votes and state Sen. Hunter B. Andrews of Hampton and former Del. Carrington Williams of Fairfax, each with about 80 committed votes.

Former Fairfax Supervisor Frederick Babson and Falls Church feminist Flora Crater appeared out of the running with 5 and 2 votes respectively. About 550 delegates were chosen as uncommitted.

Final vote totals are not yet available from the state Democratic Party, but there were no major conflicts in figures reported by the campaigns.

In the aftermath of the mass meetings, the rules for the June 9-10 nominating convention have becaome an important factor in the chances of any of the trailing candidates to win the nomination over Miller.

The proposed rules provide that any candidate receiving less than 5 per cent of the vote on the first ballot or finishing last on subsequent ballots will be eliminated from the race. They also provide that the nominee need only a majority of those voting, not a majority - 1,398 delegates - of the 2,795 authorized for the convention.

These rules tend to favor a front-runner by forcing a rapid consolidation of delegates committed to trailing candidates behind those remaining in the race.

Before the mass meetings, Andrews called for adoption of convention rules that would permit all candidates to remain in the race until one wins a majority of 1,398. Both Duval and Williams said yesterday that they support the Andrews proplosals and managers for Rufus Phillips and Conoly Phillips said they will announce their position on rules today. Rufus Phillips said last week that he "tends to favor the Andrews proposals."

DuVal said he thinks the elected officials should have been required to run for delegate spots at the mass meetings, but believes it would be unfair to deny votes to them now after they relied on the proposed rules and did not seek election as delegates.

Miller is perceived by the other candidates as being opposed to changes in the proposed rules, adopted by party committees influenced by his supporters. However, in an interview yesterday he did not take a specific stand on the rules proposals.

The stand that Conoly Phillips takes on the rules is expected to be decisive because his block of delegates appears to be large enough to provide Miller's other challengers with a majority in a rules vote on the convention floor.

"We recognize that we could be the deciding factor," Conoly Phillips' manager, Ed Mabry, said in an interview. "We have spent hours discussing it and we will make the decision tonight."

All of the candidates trailing Miller or their managers said in interviews that they believe their chances will improve after the first ballot at the convention because they expect Miller's vote to fall off after the first roll call. Some of their supporters, including some paid staff members, joined Miller caucuses at the mass meetings to ensure their election as delegates. They are committed to vote for Miller on the first ballot but free to vote their convictions thereafter.

If the trailing candidates succeed in changing the rules and in denying a majority to Miller on an early ballot, they still will be faced with the necessity of uniting behind one of the challengers.

It is clear that Miller's lead in delegates has not produced a bandwagon for him, and the other candidates and their managers said yesterday that a consolidation behind him or some other nominee probably will not take place until the delegates meet in Williamsburg.