Brussels — In recent weeks, Belgium, the Netherlands, and Ireland have all expelled East bloc diplomats as the West tries to deal with an apparent invasion of spies. The expulsions are in no way as serious as the spy scandal that shook the West earlier this year, when 47 Soviet diplomats and their families were told by the Socialist government of Francois Mitterrand to leave France.
Last weekend, Ireland ordered two Soviet diplomats as well as the wife of one of them to leave the country because of ''unacceptable activities,'' a phrase often used to indicate espionage.
On Sept. 2 the Netherlands expelled a Romanian diplomat. The Dutch newspaper De Telegraaf linked that incident to Belgium's expulsion last month of a Soviet Embassy official and four Romanians, all accused of spying.
These cases brought to more than 90 the number of Soviet citizens sent packing by NATO countries, Japan, Australia, Switzerland, and Ireland this year - up from only 49 last year and 27 in 1981. (In Thailand, 33 Soviet officials have left the country in the past two weeks, after they were named as spies by an Asian publication, according to the Bangkok Post.)
Many in the West cannot help wondering whether the situation had suddenly gotten out of hand.
The conclusion reached by most experts, in fact, is that although the ''Reds under the bed'' have not become an invasion, they have more reason now than ever to be there, and Western governments have even greater cause than before for kicking them out.
The aim of this new generation of Soviet spooks, according to officials, is to gather information on Western technology that may be useful in developing the country's still-lagging industrial base or in building more sophisticated military hardware.
So successful has the Soviet effort been in acquiring that information that ''the manpower levels they allocate to this effort have been increased significantly since the 1970s to the point where there are now several thousand technology-collecting officers at work,'' according to a United States government report released last year.
''These personnel, under various covers ranging from diplomats to journalists to trade officials, are assigned throughout the world,'' stated the report.
It is not surprising, therefore, that the Reagan administration has been leading a hard-fought campaign for the West to tighten up on the sale of high technology to the Eastern bloc. To some extent, that campaign has gained favor among American allies, forcing the Soviets to step up their intelligence efforts abroad, particularly in Western Europe.
Experts say the Soviets now obtain about 70 percent of their ''militarily valuable'' information from the West illegally. They say pressure will increase on the Kremlin to resort to even more of what diplomats politely call ''economic espionage'' as long as the Soviet system is plagued by a lack of opportunity for technical innovation and the West continues to clamp down on leaks to the East.
Those same constraints are also certain to make it more tempting for Westerners in positions of responsibility to pass on information to the Soviets, officials point out. ''There's little doubt that the Soviets have upped substantially what they pay for good information,'' a Western intelligence officer says.
That apparently was learned quickly by Eugene Michiels, a senior Belgian government official employed in the Foreign Ministry, who was arrested along with the Soviet and Romanian diplomats last month and charged with selling government documents to the East. ''It was an affair of money,'' said Foreign Minister Leo Tindemans.
Reports say Mr. Michiels earned about 6 million Belgian francs (some $113,000 ) for his work. The Belgian government has ordered a major investigation to find out whether the career diplomat may have been part of a wider network of ''moles and spooks'' working in Belgium - home to the headquarters of North Atlantic Treaty Organization, the European Community, and many multinational corporations.