Moderate leftist Salvador Jorge Blanco, 55, and his Dominican Revolutionary Party won almost complete control of the government in yesterday's election, according to unofficial returns with about half the massive vote counted.

Jorge Blanco, a dapper and energetic attorney, claimed the presidency early this morning, calling the turnout by nearly 2 million citizens "a splendid victory, which also belongs to the Dominican people."

His win represents a milestone in efforts in this politically volatile country to build democratic institutions able to tackle serious economic and social problems peacefully and the formation of a government that the Reagan administration hopes will use U.S. aid and trade concessions to become a model for other nations in the region.

Jorge Blanco immediately called on the campaign's two major losers to join him in a working coalition to succeed the Revolutionary Party government of Antonio Guzman, who did not seek reelection.

But those two losers, Juan Bosch and Joaquin Balaguer, both legendary aging former presidents of considerable personal force, were in no hurry to cozy up to Jorge Blanco and his "new generation" campaign.

Balaguer, 75, who governed with U.S. backing from 1966 to 1978, was claiming victory far into the night and made no public statements today, while his conservative supporters collected evidence of minor voting frauds. Nearly blind from glaucoma, Balaguer had appealed heavily through advertising and noisy parades just before the election to the national nostalgia for better economic times during his government.

Balaguer ran better than pollsters had expected. According to the unofficial tally, his Reformist Party was running second with 37 percent of the 1.2 million votes counted, compared with Jorge Blanco's 48.4 percent.

Third in the race was Bosch, 73, a Marxist who was overthrown in 1963 after seven months in office by a rightist military coup that he blamed on the United States. His Dominican Liberation Party, which reminded voters during the campaign of Bosch's pivotal role in sparking reforms here, was holding steady at 10.1 percent of the count. At a press conference today, he said he considered his showing "a great advance" for the party and for leftist political sentiment in the country.

But Bosch added that the new goverment of the Dominican Revolutionary Party will be able to do so little about the serious economic situation that it "will lead to a political explosion that no one can control." He said irregularities had occurred in the voting, including the apparent alteration of voter lists, but he added that he would not pursue the matter.

The more radical United Leftist Front candidate, Rafael Fafa Tavares, said his 1 percent total was "very favorable," because communist parties were only legalized just before the 1978 election and had never before been able to campaign without being shot at.

Even Jorge Blanco dissociated his Revolutionary Party from Guzman's economic policies, promising new belt-tightening measures and reforms to produce jobs as a top priority. But the Guzman government is widely credited with having depoliticized the Army, which made the peaceful elections possible.

Yesterday, the armed forces confined themselves to guarding polling places and reported today that only half a dozen people had been wounded in fist fights or disputes that broke out in various towns. The most notable incident involved a five-hour siege of the Santo Domingo newspaer El Sol, which had tried to print an election extra edition in defiance of overall censorship imposed on the voting results yesterday. Police spokesmen said the measure was taken "for the newspaper's own protection," and officials at El Sol said only that they were happy that the troops were finally withdrawn.

Military men refused at every level to discuss politics in public yesterday. A prosperous importer recalled with some awe that he had attended a dinner last week of prominent industrialists who heatedly argued politics until a brigadier general arrived, resuming only after he had departed.

"The general had made it clear he would not come otherwise," the businessman said. "This is completely different than it used to be here."