Top executives around the world received modest salary increases in 1988, and probably will get even more modest pay hikes this year, according to a study by Hewitt Associates.

Leading executives in the United Kingdom got the highest average pay hike last year - 8.3 percent - but the U.K. also had the highest inflation rate, at 4.9 percent.Key executives in Belgium received pay hikes averaging 6 percent - and the inflation rate there was a meager 1.2 percent. Canadian top executives also got raises averaging 6 percent, but they had to cope with 4 percent inflation.

Pay raises for leading U.S. executives averaged 5.6 percent, while the inflation rate hit 4 percent.

In West Germany, key executive raises averaged 5.1 percent last year, while inflation stood at 1.2 percent. In Switzerland, which experienced 1.9 percent inflation, top executives' raises averaged 4.9 percent.

In the Netherlands, the cream of the executive crop got average raises of 4.8 percent, and inflation was held to 0.1 percent.

Top French executives also got raises averaging 4.8 percent, but they got less spending power because of their country's 2.7 percent inflation rate.

Japanese executives got the smallest average pay hike - 2.9 percent. But Japan also had the lowest inflation rate - 0.7 percent.

The study, presented to reporters Monday, reviewed salary-increase data for 1988 and anticipated salary-increase information for 1989 from more than 1,900 employers in the nine countries.

The report projects somewhat smaller pay hikes for top executives this year, except in the United Kingdom and Japan.

The average senior executive in the U.K. is expected to get an 8.4 percent pay hike this year, while top executive salaries in Japan are expected to increase an average of 3.1 percent. Pay hikes for leading U.S. and Belgian executives are expected to equal last year's - 5.6 percent for the Americans, and 6 percent for the Belgians.

Projected 1989 salary increases for key executives in other countries are down slightly - to 4.6 percent for Germany; 4.4 percent for France; 5.8 percent for Canada; and 4.5 percent for both Switzerland and the Netherlands.