Belgian Premier triumphs over wave of public discontent. He has weathered most serious strikes in the country's history

The prime minister was in a buoyant mood. The Belgian national soccer team had beaten Spain the night before -- to everyone's surprise -- to reach the semifinals of the World Cup. ``It's a great day for Belgium,'' Prime Minister Wilfried Martens told a small group of foreign journalists recently, recalling that it was the first time a Belgian soccer squad had done so well in World Cup competition. ``We should feel proud.''

But even after the Belgian team was knocked out of the competition by Argentina, Mr. Martens still had reason to celebrate: For nearly two months, Martens's center-right coalition government had weathered some of the most serious public-sector strikes in the country's history. Those strikes had subsided, and it looked as if his government -- the 33rd in Belgium since World War II -- would survive the challenge.

``This has certainly been the most difficult period of my political career,'' Martens said over lunch at his residence here.

The strikes, which disrupted public transportion and postal deliveries and closed schools, were sparked by government plans to slash public spending by a whopping 195 billon francs (about $4.25 billion), or about 10 percent of the federal budget, over the next 18 months.

``I'm not surprised by the strikes,'' Martens said. ``No one likes to see budgets cut.'' This is particularly so in a nation where about 1.3 million people, or nearly one-third of the workforce and 20 percent of the voting population, are employed by the state. Many observers believe that the success of the government so far in ushering in unpopular programs without seriously jeopardizing its own existence is due largely to the personal political skill -- and courage -- of the prime minister.

``What politician would dare question the income of a fifth of the electorate?'' journalist Paul Belien asked recently. For Martens, who remains the country's most popular politician by a wide margin, reducing the size of the government till is absolutely essential to restoring the economic health of the nation. It has been his No. 1 priority since he took office as prime minister last fall for the sixth time in the past seven years.

Last year, following the creation of one of Western Europe's most highly developed welfare states, the government budget deficit blossomed to more than 12 percent of the country's gross national product (GNP) -- compared with 5 percent in the United States and less than 2 percent in West Germany. And the government's external debt was equal to 101 percent of GNP (against 21 percent in West Germany and 19 percent in France).

Martens has proposed reducing the budget deficit to about 8 percent of GNP by the end of 1987 by trimming spending on social services. Raising taxes is out of the question, as Belgium already boasts one of the highest income-tax rates in the world. But Martens does have plans for major tax reform beginning in early 1988.

Martens concedes that some social unrest could continue throughout the month of July as the government begins to put in place the spending cuts approved last month. But he is confident that the worst is past.

``We're in much better shape than we were five years ago,'' he says. ``We're tackling one of the fundamental problems of our country. But we've demonstrated that we can find solutions to our difficulties through normal democratic procedures.''