Language rift mirrors power struggle as Belgians head to polls. BELGIUM'S BATTLE

A tumultuous French-Flemish language dispute affects every strand of Belgian life - including this weekend's election. Belgians go to the polls Sunday to vote for their 33rd post-war government.

The language rift, which earlier this fall led to the resignation of Prime Minister Wilfried Martens, overshadows the country's chronic economic problems which include a public debt estimated at 8.5 percent of Gross National Product in 1987. Each of Belgium's main political parties is split into independent French and Flemish branches.

But more than language preferences are at stake. A deeper struggle for political power is under way. When Belgium was founded in the 19th-century after the Napoleonic Wars, French-speaking Wallonia dominated. Its urban, industrial economy, based on heavy industries such as steel, overshadowed rural, agricultural Flanders. Wallons occupied most of the country's posts of power in all sectors.

But in recent years, Flanders has surpassed Wallonia. The steel industry is dying and once-prosperous cities such as Liege, Namur, Charleroi now look like grimy relics of the Industrial Revolution. By contrast, Flanders has invested heavily in new technology. Its new light industries - electrical goods, appliances, chemicals, pharmaceuticals - are prospering.

Economic growth brought greater political power. Flemings now insist on using their mother tongue to prove that Flemish is just as good a voice of government as French - and Flemings just as worthy of prominence as Walloons.

Similar problems plague Fourons, a district of 4,000 with a French-speaking majority. The language issue came to a head when a French-speaking mayor of a district in Flemish-speaking Flanders refused to prove he could speak Flemish. Mayor Jos'e Happart knows Flemish, but on principle refuses to take a test proving it. His stand infuriates Flemish colleagues, who took him to court.

Last September, Belgium's highest judicial body dismissed Mr. Happart from his post. But the controversial figure continued as acting mayor.

Flemish politicians became angrier and demanded that Prime Minister Wilfried Martens get rid of Happart once and for all. Martens was unable to reach a consensus among his four-part coalition, and tendered his resignation.

Martens has kept a very low profile during the run up to the election. John Fitzmaurice, a long-time observer of Belgian politics, says, ``Martens has disappeared below the surface, which suggests he doesn't want to be too closely linked with the present coalition.''

However, Guy Duplat, chief political correspondent of Le Soir, an independent daily, disagrees. He says Martens has made it clear he is unwilling to lead a government which does not include his current liberal partners. ``He is treating these elections as a sort of referendum and asking the voters to vote `ja' for his policies of tax reform, economic austerity, and employment programs with the same coalition partners,'' Duplat said.

Another observer of Belgium's politics said, ``It is doubtful Martens will remain as premier if the present coalition is disbanded following the election.''

Latest public opinion polls predict that Martens' conservative four-party coalition will do badly in the election. Its support is down to 43.3 percent from the 50.2 percent of the last election in October, 1985. Martens' austerity program has had little impact in Wallonia and voters are more likely to adopt the socialists less stringent economic measures.

In Flanders the socialists have traditionally not done very well. This is because its people are pacifist, but the region is the site of deployed intermediate-range nuclear missiles. This week's superpower summit removes those missiles, and undecided voters may now choose to vote socialist.

The socialists may profit. Considered a moderate left-wing party, polls show them winning 31.1 percent, up from 28.4 percent in 1985.