Brussels — The Soviet Union has run into trouble selling natural gas to Western Europe.
Originally, the Soviet government offered to begin delivering some 40 billion cubic meters of natural gas a year to seven West European countries through the now-controversial Siberian pipeline beginning in the mid-1980s. But so far it has sold only half that amount - to West Germany, France, Austria, and Switzerland.
Holding out for one reason or another - or totally abandoning the idea - have been the Netherlands, Belgium, and Italy, which months ago were set to sign contracts with Moscow for shipments totaling up to 15 billion cubic meters of natural gas a year.
Things have changed. And the cost to the Soviet military and industrial machine in lost hard currency could be considerable.
''We've found we don't need Russian gas,'' a spokesman for the Dutch national gas utility said, explaining why the Dutch government has dropped plans to import about 4 billion cubic meters a year through the Siberian pipeline. ''Our reserves are larger than we had originally thought.''
For Belgium, which was in line to receive up to 3 billion cubic meters a year , the picture remains clouded.
''We're still interested in Russian gas, provided we're compensated,'' a Belgian Energy Department official said. Talks between the two sides have been suspended since Moscow failed to award a single pipeline construction contract to a Belgian company. Low-level contacts continue.
Also restraining the Belgians: New energy forecasts show reduced gas requirements over the next two decades.
The Italian government - which recently signed a 25-year contract with Algeria for 4 billion cubic meters of natural gas a year beginning in 1983, rising to 12 billion cubic meters by 1986 - has been divided for months over whether to sign a contract negotiated with the Soviets earlier this year for delivery of 8.5 billion cubic meters a year beginning in 1984.
Some Italian Cabinet members oppose new business deals with the Soviets on political grounds; others consider the need for new supplies (despite the Algerian contract) more important than political issues. Most Italian energy officials say the agreement will be signed eventually.
It remains to be seen what a failure to sell nearly 20 billion cubic meters of natural gas to Western Europe would mean to the Soviet Union in cash terms. Also open to question is the effect of cutbacks of some 5 billion cubic meters from initial requests by the four countries that have signed deals.
Reagan administration officials have argued that hard-currency earnings for the Soviet Union - based on sales of 40 billion cubic meters of natural gas to Western Europe a year - will amount to some $10 billion annually. But energy experts at the Paris-based International Energy Agency emphasize that the Soviets will be fortunate if they pocket $2 billion a year after exploitation investments.
''Let's just say that if the Soviets can't sell half of what they had originally planned to sell to Western Europe, their profit will be cut considerably,'' a European energy expert said. ''That's something the Americans shouldn't forget.''