SOFIA, BULGARIA, JUNE 10 -- Reform Communists moved out to a commanding lead tonight in this country's first free election in 58 years.

The apparent victory of the reform Communists marks an atypical end to Eastern Europe's historic season of the ballot.

Only in Bulgaria, which for 45 years was the most quiescent and obedient country in the former Soviet Bloc, have reform Communists given a well-organized opposition a crack at taking over the government and then been handed back power by the voters.

International observers said they saw no major or systematic irregularities in today's vote.

Projected results tonight showed the Socialists, as the Communists have renamed themselves, winning about 48 percent of the vote in parliamentary elections. The main opposition group, the Union of Democratic Forces, won about 32 percent of the vote.

These results are based on projections of voting results from 250 scientifically selected precincts across Bulgaria. The projections were done by Infas, a West German polling firm that has accurately called the Romanian, East German and Czechoslovak elections. Other groups' projections produced similar results.

Leaders of the Socialist Party have repeatedly emphasized that they want to invite the opposition to join them in forming a broad coalition government. Bulgaria's economy, like many in Eastern Europe, is on the brink of collapse. Socialist leaders say that Bulgaria can only expect social peace and support from Western donors if they can pull the opposition into the government.

On a hot, sunny day, voters swarmed early to polling places in schools and auditoriums around the country. A spokesman for the Central Election Commission said the national turnout was more than 80 percent. He described the atmosphere at voting centers as "calm, tranquil and proper."

Today's vote, along with a runoff next Sunday, will choose a new 400-seat assembly. Half of the deputies will be selected by direct vote and half on a proportional system based on their showing in 28 regions. The main work of the new assembly is to write a new constitution. After 18 months, it can decide whether to dissolve itself for another election or continue for a four-year term.

The West German firm Infas projected tonight that of the 200 seats chosen by proportional vote, 100 were won by the Socialists. It said that the Union of Democratic Forces won 67 seats and the Agrarian Party 16. A Turkish minority party, the Movement for Rights and Freedoms, made an exceptionally strong showing, winning 17 seats, according to the projection.

In several voting places visited today in central Bulgaria, the presence of observers from the three main parties and the obvious secrecy of the voting process seemed to dispel fear.

American observer groups, which operated in 12 cities and checked about 10 percent of the country's polling places, reported this afternoon that they saw no serious irregularities.

Human rights groups and the U.S. government had complained that the election campaign was marred by Socialist Party intimidation and threats against voters, particularly the elderly. But one member of the observer team said today that he was pleasantly surprised by how well the voting appeared to have been conducted.

"I can sense the democracy. There is no inertness, no intolerance like in the elections under {deposed dictator Todor} Zhivkov," said Radoslav Stefan Karaivanov, chairman of the election committee at a polling place in Veliko Turnovo, an ancient city of 70,000.

"I am not afraid. I voted for the {opposition} Union of Democratic Forces because they have a new way of thinking. The Communists had power for too long," said Silvia Nanova, 23, a salesclerk.

The benign voting atmosphere, which one election committee supervisor described as "like a festival," was in upbeat contrast to the suspicion and fear that election observers noticed last month in neighboring Romania.

There, the former Communists who overthrew dictator Nicolae Ceausescu won an easy victory against a weak, disorganized opposition. Here in Bulgaria, the Union of Democratic Forces, a coalition of 16 former dissident groups, ran a strong campaign.

Taking advantage of 20 minutes of daily television time guaranteed by an agreement with the Socialists, the Union hammered away at one message: that communism has ruined the economy and terrorized its people and that 45 years are enough.