Brussels — When the King of Belgium arrived for lunch, all the commercial bankers stood up and watched as the blue-suited, smiling monarch took his seat. To their surprise, he had something of substance to say and not just niceties. But it wasn't new.
King Baudouin gave the bankers, representing some 113 of the world's largest banks and literally trillions of dollars of assets, the view of the European Community on issues to be discussed at the Williamsburg, Va., summit this month.
''We find it essential,'' he told the International Monetary Conference Wednesday, ''that industrial countries should really take into account the effect of their economic policies on other countries.
''It is necessary to aim at a further reduction of real interest rates, particularly in the United States.
''The authorities representing the currencies of the European monetary system , the United States, and Japan should cooperate towards greater monetary stability.''
Only two days earlier, Wilfried Martens, the prime minister of Belgium, had made similar points in his talk to this group of powerful bankers, gathered for their annual international monetary conference here.
''The lack of harmony between fiscal policy and monetary policy unduly raised US interest rates and hampered the recovery process,'' he said.
The Europeans habitually complain about US economic policies; in the early years after World War II they complained about the dollar's strength and the shortage of dollars. Then the dollar was too weak and in surplus, the Europeans said, but they resisted devaluation of the dollar until the 1971 international monetary crisis.
Then the Europeans grumbled about the US not tackling inflation as the American consumer price index started rising at double-digit rates. However, they can't claim today that the US is doing nothing about inflation, so they object to its methods.
It is sometimes hard for American officials and bankers to know whether to take the Europeans seriously or not. There is often the suspicion that the Europeans are trying to shift the blame for their own economic mistakes to the US.
Said Norman A. Bailey, senior director for national security planning at the White House's National Security Council, during a press conference here: ''It behooves us all . . . to concentrate more attention on the motes in our own eyes than to scapegoat other countries.''
One reason the French are expected to seek a confrontation with the US at the Williamsburg summit is to draw domestic attention away from their own basic economic-policy mistake.
The French Socialist government launched an expansionary economic program when they came into power in the spring of 1981, hoping to avoid any increase in unemployment. But the move was badly timed. France's trading partners were still going into a slump. Inflation in France continued in the 14 to 15 percent area, while it dropped rapidly in other European countries and in the US. France's international payments sank into the red, forcing the government and nationalized companies to borrow heavily abroad. The nation's credit is now so bad that this week it was announced that the European Community would borrow about $3.7 billion on behalf of France. The money will be used to support an austerity program launched belatedly this spring by the Socialist government. Moreover, the franc has had to be devalued a few times.
The French blame their problem on the high US budget deficit, which prompts high real interest rates (after removing inflation), and on a too-strong dollar. This, they maintain, is preventing an adequate recovery in Europe.
''It's not the Americans who pay for the budget deficit, it's the Europeans, notably the French,'' said Laurent Fabius, the French minister of industry.
Some high American officials are fed up with this sort of criticism, even though they, too, would dearly prefer a reduced budget deficit. One wondered whether this spring's summit might be the last for some years if it turns into a noisy, counterproductive confrontation. It is argued that top administration officials spend too much time preparing for the summits and that the results are not worth the fuss.
In the past, American administrations have sometimes welcomed European criticism when it reinforced their arguments in a dispute with Congress. The Federal Reserve system, which has been pressing for a tighter fiscal policy, is not unhappy to have European allies.
But the White House is not keen on seeing the summit turned into a political hassle.
In economic terms, the European complaints have some validity. Martin Feldstein, chairman of President Reagan's Council of Economic Advisers, recently gave a talk explaining how high deficits maintain high interest rates, which in turn stimulate inflows of foreign capital and a strong dollar.
The French industry minister objected to this flow of money to the US. High US interest rates mean that France and other European countries must maintain their own interest rates higher than they would like. Lower rates, European officials figure, would help stimulate their economies.
However, for France and Belgium to complain about US deficits is something like the pot calling the kettle black. The US deficit amounts to about 6 percent of the nation's gross national product. It is about the same in France if all public-sector borrowing is included. The deficit in Belgium was 16 percent of the GNP last year. These deficits also help hold up interest rates, noted one Belgian economist.
Admitted one skeptical French commercial banker about his government's position, ''It is all political.''