Brussels — Belgium's bankers believe that progress is springing from the nation's economic adversity. ''In the last 21/2 years we have made a lot of adjustments,'' said Wilfried Janssens, an economist and director of financial functions at Kredietbank.
''Confidence in the Belgian franc is much larger than two years ago,'' noted Rene Deweeck, an economist and deputy manager at Banque Bruxelles Lambert.
Added Xavier Malou, managing director of the Societe Generale de Banque, ''We have noticed a certain change of climate. Belgium is now more attractive for multinational corporations.''
Two or three years ago Belgian bankers were gloomy. Industry was not adequately competitive in international markets. The balance of payments was in serious deficit, equivalent to 5 percent of the nation's gross national product (GNP). Business profits were low. A massive budget deficit was growing. But instead of devoting top priority to the economy, the government was enmeshed in the language and cultural dispute between the nation's French-speaking Walloons and its Dutch-speaking Flemish.
In effect, Belgian business was running down. Between 1970 and 1981, industrial employment decreased 25 percent, a reduction that was twice the European Community average of 12.2 percent. Moreover, the nation was living beyond its means, borrowing heavily abroad to cover its international payments deficits.
Since then three developments have cheered the banking community:
* Prime Minister Wilfried Martens, after the general elections of November 1981, formed a coalition government of the Social Christians and the conservative Liberals willing to tackle the nation's economic problems.
''There is a new image, a new spirit for this government,'' said Mr. Deweeck. ''It is more business oriented. It is deeply interested in the private economy.''
* At the beginning of 1982 the government devalued the Belgian franc by 8.5 percent within the European Monetary System.
Astonishingly, according to Kredietbank's Mr. Janssens, this devaluation had a rapid impact on the competitiveness of Belgian exports. ''Probably in 1984 our account of the balance of payments will be in surplus.''
The devaluation was accompanied by a temporary price freeze and wage controls.
* The government ended Belgium's system of automatic wage indexation, whereby wages were increased in line with the inflation rate. ''This was an important cost factor for our industry,'' said Mr. Malou of the Societe Generale de Banque.
What this change has meant is that the real wages of Belgian workers have been cut as prices continued rising. Wages have been rising 1 or 2 percent, compared with an 8 or 9 percent annual rate about two years ago. In fact, under a new law the government can intervene in wage bargaining ''by all useful means'' if Belgian wages should increase faster than the weighted average of the nation's seven main trading partners.
With costs rising more slowly, Belgian companies have been able to improve their profitability sharply.
At this point, Belgian economists expect a modest recovery this year. Mr. Deweeck predicts a rise of only 0.2 percent for GNP and about 2 percent next year. Mr. Malou expects an increase of more than 1 percent this year. ''We expect to follow what is happening in West Germany,'' he said.
Prices, which increased some 8.7 percent in 1982, will climb about 6.5 or 7 percent this year and only 5 percent in 1984, Mr. Deweeck figures. But unemployment, a very high 14 percent, is not expected to drop rapidly.
The recovery will be export led, the economists reckon. Exports climbed 2.5 percent in real terms last year and will rise another 3.75 percent this year, according to Mr. Deweeck. ''One worker out of 2 in Belgian manufacturing is working for foreign trade,'' he noted.
The Martens government has succeeded in holding the line on the budget deficit. Mr. Janssens says the deficit, as a percent of GNP, will drop from 16 percent in 1982 to a still high 14 percent by 1984. ''We can handle this, because the national savings rate is so high,'' he said. With a generous welfare system and heavy subsidies for declining industries, tax revenues at all levels of government amount to about 47 percent of GNP.
Speaking of the government's efforts to restore the competitiveness of Belgian business, Prime Minister Martens said last month: ''We have sinned in this respect . . . , but we repented, and we are still doing penance for our past sins.'' Mr. Martens hopes world recovery will help lift Belgium from its period of economic penance.