Vinicio Cerezo, a Christian Democrat with a history of opposition to military rule, easily won the first round in Guatemala's presidential election today and called on his nearest opponent to drop out and avoid a runoff vote.

Roberto Carpio, the National Center Union leader who finished a distant second in yesterday's voting, refused to concede and said he would seek support from other parties to pursue his challenge.

Barring a later agreement between the two front-runners, therefore, the first-round results set the stage for a runoff vote Dec. 8 matching Cerezo, 42, a veteran center-leftist, against Carpio, 54, politically a relative newcomer.

Unofficial results from the Supreme Electoral Tribunal tonight gave Cerezo 444,942 votes, or 39 percent, to Carpio's 233,812, or 21 percent, with 64 percent of the valid votes counted. Several parties shared the remainder.

The eventual victor is scheduled to be sworn in Jan. 14 as Guatemala's first elected civilian president after 15 years of direct or indirect military rule and a generation of military dominance only occasionally questioned since a CIA-orchestrated coup d'etat in 1954.

Whether Cerezo or Carpio, the new president faces the difficult task of easing the military away from political power without provoking opposition among officers that could result in another coup.

Against that background, Cerezo today hailed the role of the current military chief of state, Gen. Oscar Humberto Mejia Victores, and said there was no Army intervention in yesterday's balloting.

"We have to recognize that the attitude of the Army in the electoral process is historic," he added at a news conference. "This is a big step for real democracy in Guatemala."

A team of U.S. observers headed by Sen. Richard G. Lugar (R-Ind.) declared that the voting was organized without the fraud that has marked Army-run elections here in the past. "It is the unanimous conclusion of this bipartisan delegation of elected officials and private citizens that these contests were fairly and efficiently conducted," Lugar said in a statement.

Cerezo called on Carpio to forgo the second round because, he said, it would be only "a formality." He offered to include followers of Carpio in a government.

Carpio refused to rule out joining forces with Cerezo later, if a bargain could be struck, but said:

"We consider it is absolutely necessary that the party that is going to govern have an absolute majority . . . . We are determined to go to the second round."

Guatemalan electoral law provides for a runoff unless a candidate wins an absolute majority in the first round. The voting also was for a 100-seat Congress.

Political observers said the outcome demonstrated that Cerezo increased his strength in the capital, where he traditionally has been strong, and in parts of the countryside, where more conservative parties long have prevailed.

In last year's Constituent Assembly elections, the two main parties were considerably closer, with the Christian Democrats winning 16.4 percent of the vote and the National Center Union 13.7.

Holding the third rank in today's count, with 157,144 votes, was Jorge Serrano of the Democratic Party of National Cooperation, a new group. In fourth place with 130,230 was Mario Sandoval of the National Liberation Movement, the traditional right-wing party with ties to landowners and conservative military officers.

Guatemalan political observers said that Serrano's organization is thought to be unable to deliver many votes in a second round but that Sandoval could bring a number of his followers to any alliance then. Both Cerezo and Carpio said they plan to seek allies for the runoff.

Abstensions accounted for about 29 percent of the 2.7 million registered voters, which Guatemalan politicians said was normal here. Only half as many blank ballots, often used as a protest, were cast than in the last vote.

Guatemalan law requires citizens to vote under penalty of fines or other administrative sanctions, but these have been applied infrequently in the past.