The government estimated today that 78 percent of Polish voters participated in yesterday's elections, only slightly more than in local elections last year and well below the turnout recorded in past communist elections of a legislature.

The estimate, released at a news conference by government spokesman Jerzy Urban, fell below the level sought by party and government officials and suggested a continuing political stalemate between the government of Gen. Wojciech Jaruzelski and its opponents in the banned Solidarity union, western diplomats and other analysts here said.

Solidarity leaders, who called for a boycott, dismissed the government turnout figures as false. A communique from the union's underground said calculations based on observations of polls showed that turnout in Warsaw was only 60 percent, and in Gdansk 52 percent. Lech Walesa said the elections "are not plebiscites for or against the authorities. They don't make anyone credible, and they do not deprive anyone of his credibility."

Government authorities and the official media described the elections for the 460-member Sejm as a show of public support for Jaruzelski's policies. "Society in its overwhelming majority showed attachment to ideals that are fundamental to Poland's socialist politics," the communist party daily Trybuna Ludu said in a front-page editorial.

Authorities gave no indication whether the results would prompt measures of liberalization hinted at by Jaruzelski and other officials before the elections on condition of a high turnout. Jaruzelski said last month that strong voter support might lead to an amnesty for the more than 280 political prisoners. Since then, however, officials and Polish media have played down the comment, stressing that an amnesty would have to be considered and approved by the new Sejm.

Urban, who last night jubilantly described the turnout as a "boycott of the boycott," said today that results from 29 of Poland's 49 provinces indicated that more than 20 million of the nearly 26 million voters had cast ballots. He said the government estimated a final turnout figure of 78 percent, compared with 74.95 percent in June 1984.

The official news service PAP reported later that counting in districts was complete and that a "preliminary unofficial estimate" put the turnout at 78.8 percent.

The figures appeared close to the stated expectations of several ranking party and government officials, who said in interviews last week that they hoped for 79 or 80 percent. The figure in 1980, the last legislative election, was 98.9 percent.

Urban said the turnout had been reduced by such factors as local political problems in the countryside and public disinterest in politics.