President-elect Vinicio Cerezo likes to tell U.S. reporters that he decided to enter politics at age 12 when the CIA backed a 1954 rebellion that overthrew a leftist government in Guatemala.

"I remember sitting on the branch of a tree and crying because U.S. planes provided to the insurgents were flying over Guatemala City. We lost a sense of liberty and of law. I decided then to try to get it back," Cerezo said Saturday.

Now, however, Cerezo will be seeking U.S. and other foreign aid to revive this country's moribund economy and shore up its first civilian government since 1970. He announced today that he will visit Washington on Dec. 17 for talks with members of Congress and with administration officials who "very probably" will include Vice President Bush.

"They've owed it to us for a long time," Cerezo said of the U.S. aid.

Cerezo, a lawyer who calls himself a moderate leftist, swept to a landslide victory in yesterday's runoff election against his center-right opponent Jorge Carpio.

Cerezo received 1,133,517 votes, or 68.4 percent of valid ballots, compared to Carpio's 524,306 votes, or 31.6 percent, according to complete returns issued by the Supreme Electoral Tribunal.

Nearly 8 percent of ballots were declared invalid because they were deliberately spoiled or left blank. Turnout was 65 percent, down from 70 percent in the first-round election on Nov. 3.

In many respects, Cerezo's career is similar to that of President Jose Napoleon Duarte in neighboring El Salvador. Both are Christian Democrats who suffered through long periods when right-wing military regimes employed brutal repression and vote fraud to keep even moderate civilians from power.

Cerezo himself has survived at least three assassination attempts and carries a sidearm for self-defense. In 1979 he shot back at assailants who opened fire outside the Christian Democrats' heavily guarded party headquarters.

Trim and athletic at 42, he also holds a black belt in karate but says he practices martial arts for "personal discipline" rather than to protect himself. Since 1970, Guatemala's Christian Democrats have lost 400 party leaders at various levels to assassinations, according to party officials.

"I have gone ahead in my time because I lived in the difficult times in Guatemala, and I survived," he said yesterday after the polls closed.

Cerezo, like Duarte, will have to govern in an uneasy partnership with the armed forces. The military retains ultimate authority here. Cerezo jokes that should his government fail, he would end up in Miami because a coup would force him into exile.

Trying to start off well with the military, Cerezo and his fellow Christian Democrats have gone out of their way to praise the armed forces for agreeing to hand over power on Jan. 14. The president-elect said several times on television last night that Gen. Humberto Mejia Victores, the current chief of state, "is going to pass into history as the military chief who recognized that the Guatemalan people should choose their own rulers."

But Cerezo's overwhelming victory margin should strengthen his hand in dealing with the armed forces, and he also said pointedly that it was time for the military to return to the barracks and be the "servant" of the people. "The government of Mejia Victores did not have the popular power that we have," Cerezo said.

The Christian Democrats triumphed because of Cerezo's personal appeal and because the political right was divided. He benefited from a bandwagon effect after the first round, where he polled nearly twice as many votes as Carpio, his nearest rival in a field of eight.

Carpio, a newspaper publisher, conceded early this morning and promised to lead the opposition in a "constructive, vigilant and critical" manner.

Cerezo's informal style seemed to have gone over well with the voters. He frequently wears denim jackets and said that he wanted people just to call him "Vinicio", his middle name, even after he becomes president. His real first name is Marco, but he rarely uses it.

Critics charge that Cerezo has never been anything except a professional politician and thus lacks the experience of having governed. Conservatives have tried to label him a communist, but he has said repeatedly that he would not risk alienating the military or the business sector by nationalizing private companies or instituting land reform.

The left, on the other hand, charges that Cerezo has sold out to the military and will not be able to curb human rights abuses. His success in this field will be important for his effort to obtain aid both from the U.S. Congress and from West European governments.

Cerezo says that he needs $300 million in economic aid in the first six months of his administration, a figure more than four times that appropriated by the United States for Guatemala in the fiscal year recently begun. In his quest for support, he also plans to travel before his inauguration to Western Europe, Mexico and Venezuela.

Cerezo has been cagy about his position on the critical issues of how far Guatemala would go to satisfy U.S. desires in order to obtain economic aid, and whether he even will seek a resumption of military aid, suspended in 1977 because of human rights concerns.

He said today that he would not oppose congressional requirements for improvements in the nation's human rights record, saying that was one of his government's goals. He stressed that Guatemala would not sacrifice its current neutralist position within Central America and adopt a more critical position toward Nicaragua in order to win Reagan administration support. But he endorsed one of the United States' key criticisms of Nicaragua by saying that Nicaragua's Sandinista government had "problems" in the areas of political pluralism and democratization.