Conceding for the first time that he apparently lost a close Virginia U.S. Senate election to Republican John W. Warner, Democrat Andrew P. Miller said through his lawyer yesterday he will seek a court order today giving him the right to inspect election tally sheets in a search for possible errors or irregularities.

According to an unofficial count, Warner defeated Miller by 5,190 votes out of more than 1.2 million cast in the Nov. 7 election.

Yesterday, Miller aides distributed copies of a suit to be filed in the state Circuit Court in Richmond alleging that his campaign committee ahs been denied access to the tally sheets by Joan S. Mahan, secretary of the State Board of Elections.

The suit, prepared by Miller's lawyer, former attorney general Anthony F. Troy, contends that Miller has a right under freedom of information laws to inspect the tally sheets immediately. Mahan has used a provision in the Freedom of Information Act to delay giving a final answer on access to the tallies until Nov 24, three days before the official canvass of Senate election votes by the Board of Elections.

Troy argues in the suit that such a delay could prevent Miller's campaign committee from completing its own "self-check" of election results before the canvass. After the official Nov. 27 vote count, the complaint said, Miller probably would have to ask for a recount of the votes to bring any inaccuracies or irregularities to light.

Because he apparently lost by less than 1 percent of the total vote, Miller would have an automatic right to a recount. However, if he loses the recount he would have to pay for its costs, estimated by Mahan to be about $125,000.