With apparent ease, the Soviet Union has circumvented a United States embargo on machinery that Western officials claim could be used to manufacture nuclear missile launchers, buying the equipment elsewhere, according to Soviet diplomats.
''It caused a brief delay in our plans,'' a Soviet trade offical on a visit to Brussels said last week about a US ban on the sale by Belgium of a $1.7 million machine to the USSR earlier this year. ''But it was nothing more serious than that.''
A Soviet official who preferred to remain anonymous would not name the country that had sold Moscow the milling and boring machine. ''But the Belgian equivalent was less expensive,'' he said.
Belgian officials, meanwhile, revealed that Moscow is seeking roughly $127, 500 in compensation for nondelivery under a contract signed between the Soviet Union and the small Belgian machine manufacturer Pegard.
Earlier this year, the US learned that Pegard had contracted to sell one of its highly sophisticated milling and boring machines to the Soviet Union. The Reagan administration immediately began to pressure the center-right Belgian government to deny the firm an export license, arguing that the ''end user'' would be the Soviet military. (Belgian Foreign Minister Leo Tindemands later contended that the machine would be used to help build launchers for SS-20 nuclear missiles) and the administration offered to find another buyer for the machine so Pegard would not be made to suffer.
Weeks passed without a buyer other than the Soviet Union appearing on the horizon.
Then in early August the Belgians announced that their Army could use the Pegard machine - but that it couldn't afford $1.7 million. The Reagan administration stepped into the picture again, saying it would kick in $700,000 toward the purchase price. The US and Belgium signed the deal on Aug. 9.
Soviet officials who were in Brussels last week to promote trade between Belgium and the USSR said the incident had not discouraged them from doing business with Belgium.
Soviet trade with Belgium last year totaled about $1.8 billion - more than with the United Kingdom.
''We're ready to buy machines even more sophisticated than the Pegard machine ,'' said a Soviet trade expert. ''We don't want anything obsolete.''
Nearly ready for signing is a contract for the sale of a multimillion-dollar Belgian food processing plant, officials said.