BRUSSELS, Belgium (AP) _ Prime Minister Wilfried Martens' center-right government lost ground to the Socialists in nationwide elections but held on to a slim parliamentary majority, according to nearly complete results Monday.

They showed the coaltition lost five seats but held 110 in the 212-member Parliament.

Results of Sunday's elections were based on 94 percent of the 3,691 polling stations counted, the Interior Ministry said. Final results were not due until later Monday.

The elections made the opposition Socialists the largest single political force in Parliament, with 72 seats. This could return it to government after a six-year absence, depending on alliances.

When earlier figures showed Martens' coalition of Christian Democrats and Conservatives losing at least five legislative seats, he called the trend a setback for his plans for continued austerity, his key campaign issue.

He blamed political conflict between French-and Dutch-speaking Belgians for his coalition's poor performance.

''I had not expected the verdict ... would be as severe as it is. With these statistics, it is not possible to form a stable and coherent government,'' Martens said on television.

''Tomorrow (Monday) we will see how many seats the coalition has,'' he said. ''It is then the task of the monarch to start consulting'' political leaders with a view to forming a new government.

The results showed the Dutch- and French-speaking wings of Marten's Christian Democrats had dropped to 62 seats from 69.

Polls were open from 8 a.m. to 1 p.m. About 7 million people had been expected to vote in this bilingual nation of 10 million, where balloting is mandatory.

Eleven of the 29 parties in the elections held seats in the previous Parliament. In Belgium, all political parties are split into a French-speaking party and a Dutch-speaking party.

Martens, 51, called the elections on Oct. 19, the day his coalition collapsed in a linguistic dispute.

Pre-election polls had predicted that the four-party coalition, the seventh Martens has headed since 1979, would lose its majority. The polls predicted gains for the Socialists.

The Dutch-speaking Socialists are led by Karel van Miert. In Wallonia, the Francophone Socialist party is led by Guy Spitaels.

In the last elections in 1985, Martens' coalition got 50.2 percent of the vote and won 115 of the 212 legislative seats, a gain of two over the 1981 elections. The Socialists got 28.4 percent of the vote, or 67 seats, in 1985.

Whatever coalition emerges from the voting, talks to form a new government, Belgium's 35th since World War II, will be difficult.

The next Parliament is to make sweeping changes in the constitution to give more autonomy to Flanders, Belgium's Dutch-speaking northern half, and Wallonia, the French-speaking southern region.

The changes are considered necessary to end the ancient bickering between Dutch- and French-speakers.

Since 1980, the two regions have had limited powers of autonomy in regional economic, social and cultural matters.

The next Parliament may transfer education from the national government to the regional administrations and create a special court to resolve linguistic disputes.

It was a language dispute - the refusal of the militant Francophone mayor of a Flemish farming village to speak Dutch as required by law - that brought down the government Oct. 19. The same argument paralyzed Martens' government in October 1986, but the issue was temporarily resolved that time.

The main political parties favor making Belgium a more federated state, but the country's two linguistic camps hold differing views on how to achieve this.

There are about 5.5 million Dutch-speakers in Belgium and 4.5 million Francophones. Although language arguments surface regularly in politics, the election campaigns of most parties focused on economic issues.

The four coalition members and most of the opposition parties stressed the need to reduce Belgium's budget deficit.

Martens' outgoing government has reduced the deficit from 13 percent of gross national product in 1982 to 11.3 percent, or $16 billion. If re-elected, it plans to slash it to 7.4 percent, or $11.6 billion, next year.

Martens also cut the annual inflation rate from 8.4 percent in the early 1980s to 1.3 percent.

But opposition parties said the government was not doing enough to reduce unemployment, hovering around 12 percent of the work force, and to bolster economic growth, which is expected to decrease this year.

Almost all of the 11 parties in Parliament also agreed on a plan to cut taxes. The outgoing coalition said it wanted to privatize large state companies.