GUATEMALA CITY, JAN. 7 -- Jorge Serrano Elias, a Protestant evangelist and businessman, was declared president-elect today after winning 68 percent of the vote in Sunday's runoff election.

Considered a relative outsider before the election's first round in November, Serrano trounced conservative newspaper magnate Jorge Carpio Nicolle, who had 32 percent of the nearly complete count.

Serrano is to take office Jan. 14 in the first case of a Guatemalan civilian peacefully receiving power from another civilian. Guatemala only returned to elected civilian rule five years ago, when President Vinicio Cerezo and his Christian Democrats swept to power, amid a wave of optimism after decades of military dictatorship.

But the experiment in democracy has left many disillusioned. Cerezo's accession in 1986 raised high hopes, but he leaves a faltering economy and increased crime, political violence and corruption. The army retains much of the real power and a 30-year guerrilla war in the mountains drags on.

Less than half of those registered turned out to vote. To cheering supporters, Serrano announced that he would form a government of national unity. He promised to negotiate with leftist guerrillas and call an assembly to revise the constitution.

Human rights activists estimate that 100,000 suspected leftists have been killed here in three decades.

U.S. officials say they hope Serrano will take a strong hand as commander-in-chief of the army. Last month, the State Department cut military aid because of the army's deteriorating human rights record, and officials say the army could lose up to $20 million in the pipeline. The United States still supplies over $100 million in economic aid.

But opposition politicians are skeptical that any civilian can stand up to the military. "This is Latin America," said Jorge Skinner Klee, a deputy for the defeated National Centrist Union. "The new president will have to make a deal with the army."

Serrano has been careful not to antagonize the military which he has praised as being "very professional."

"The military have power not through their arms, but through an infrastructure that goes from the Defense Ministry to the smallest hamlet in the country," said Serrano in a preelection interview. "For 170 years the country has depended on this military structure and you cannot change that overnight."

Serrano served in the military government of another evangelical Protestant, Gen. Efrain Rios Montt, in the early 1980s. In part he owes his victory to the network of evangelical churches, many of them offshoots of churches in the United States, that have mushroomed in Guatemala in the last 10 years at the expense of the predominant Roman Catholic Church.

Rios Montt, who headed the opinion polls during the election campaign, was barred from running because he had previously held power through a coup. Serrano took up the general's law-and-order platform.

Serrano has friends in the conservative wing of the U.S. Republican Party and is a close associate of Sen. Jesse Helms (R-N.C.), according to an informed diplomat.

More recently, Serrano headed a broad-based delegation that held direct talks with the rebels in Oslo last year. He emphasized that any constitutional changes would have to be carried out legally and would depend on the country's other social forces, not just the rebels.

The guerrillas, whose numbers have dwindled to a few thousand, called on people to boycott the presidential vote, and in some areas rebel fighters barricaded roads. They are unlikely to disarm while human rights violations remain rampant. There as an average of at least one political killing a day, according to the government's own human rights monitors.

Serrano's party, the Solidarity Action Movement, formed in 1987. It won less than a sixth of the seats in the new Congress. Serrano is expected to name leaders from other parties to his cabinet. These will almost certainly include Alvaro Arzu, the leader of the right-wing National Advancement Party, and several figures from the departing Christian Democrat administration.

Much of Guatemalan's disillusionment with democracy arises from the faltering economy, with inflation at a record 60 percent and an alarming rise in violent crime.

A visit to Guatemala City's garbage dump gives an idea of the problems the new president will inherit. The refuse forms an enormous rotting cliff at the entrance to a steep gorge. Mangy dogs and clouds of vultures compete with hundreds of people to survive off the trash. A whole shanty town has grown up at the dump. Working 10 hours a day, people can make about 50 cents collecting recyclables.

"More and more people come here to live," said Carlos Mendez, 42, who has lived and worked at the dump for 26 years. "They have to leave their land when the landlords want to grow sugar cane. The politicians make lots of promises. But for the poor, things get worse."