The Belgian government has ordered the expulsion of several diplomats and arrested a senior official in its Foreign Ministry for their alleged involvement in a case of economic espionage, Foreign Minister Leo Tindemans announced today.

Tindemans refused to identify the diplomats in a television interview, saying he wished "to avoid diplomatic difficulties."

But Belgian television reported six hours later that two Romanians and one Soviet already had been expelled from the country. Officials at the Romanian and Soviet embassies here refused to comment.

Belgian radio said the government had expelled five diplomats, but this number could not be confirmed today.

"It is clearly a case of economic espionage," Tindemans said.

The foreign minister also confirmed that Eugene Michiels, a trade specialist in the Foreign Ministry, was arrested about a week ago for selling information to the diplomats who have been ordered out. Michiels, 60, had been responsible for coordinating Belgian trade with the European Community and with Comecon, the Soviet Bloc's common market.

Tindemans said, "We suspected Michiels for quite some time before his arrest but did not want to arouse his suspicions." Michiels' motive, Tindemans said, was financial gain, not ideology.

Officials at the Polish, East German and Czechoslovak embassies would not comment on the affair. A spokesman at the Bulgarian Embassy said no Bulgarians were involved.

The socialist Dutch-language daily newspaper De Morgen, which broke the story today and prompted Tindemans' announcement, also linked the affair to the Soviet Bloc, United Press International reported. "The nationality of the diplomats is not known, but it can be reasonably assumed they are from one of the East Bloc nations," the paper said.

Michiels, who is now being held in a Brussels prison, joined the Foreign Ministry in 1959. In 1970 he became director of the department that, among other things, helps organize meetings among the foreign ministers of the European Community, as well as the regular summit meetings between leaders of those countries.

Belgium's expulsion of Soviet Bloc diplomats follows a string of similar actions by Western European governments this year.

In the past seven months, every North Atlantic Treaty Organization member in Europe, with the exception of Luxembourg and Portugal, expelled or arrested men accused of being Soviet spies. The men were accused either of stealing economic or technological information, or of campaigning aggressively to block the deployment at the end of this year of nuclear missiles in Western Europe.

In July, Switzerland expelled Vladislav Istomin, a vice consul in Geneva described as a spy specializing in technological and economic information.

Denmark expelled Yevgeny Motorov, head of the Soviet KGB's field section on Copenhagen for science and technology.

In a spectacular show of force that may have inspired other governments to crack down on KGB spy operations, France ordered 47 Soviet citizens to leave in April.

For Belgium, this week's expulsion was the second this year. In May, Yevgeny Mikhailov, managing director of Elorg, S.A., a joint Belgian-Soviet computer firm near Antwerp, was ordered to leave, as was his predecessor seven years ago.

Expulsions of Soviet diplomats from western countries have increased dramatically during the past two years. Ninety have been ordered home this year, compared with 47 last year and 27 the year before.