BONN, DEC. 21 -- The U.S. Embassy in Bonn this week gave the German government a list of 50 German companies believed to be violating the U.N. embargo against Iraq, a spokesman for Chancellor Helmut Kohl said today.

The spokesman, Dieter Vogel, said Germany already has cleared most of the companies on the list of any suspicion but is investigating other companies to see if they violated export controls, including those imposed against Iraq by the United Nations Aug. 6 in retaliation for that country's invasion and occupation of Kuwait.

A U.S. Embassy spokesman, Cornelius Walsh, refused to comment on the existence of a list.

But U.S. government sources said that the United States, using information obtained from intercepted Middle East telephone and fax communications, has given Germany evidence that some companies are continuing to do business with Iraq.

The German weekly news magazine Der Spiegel, quoting unidentified sources, will report in its next issue that the latest illegal exports involved shipments to Iraq through third countries, including Iran, Turkey and Jordan.

Der Spiegel also reports that a German company called Interatom has provided Iraq with highly sensitive nuclear technology. The magazine, quoting unnamed "officials" and "experts," said Interatom provided crucial training in uranium enrichment to Iraqi atomic researchers and machinery to be used in the construction of a nuclear test facility.

A spokesman for Interatom, which is owned by the German electronics and computer giant Siemens, denied the allegations as "completely false and baseless."

"We have never made deliveries or {provided} training in the field of nuclear technology," spokesman Hartmut Meyer told reporters.

Interatom, which builds atomic reactors, signed a contract in mid-1989 with the Industrial Projects Co. in Baghdad to provide the Iraqi firm with training and advice, the German company confirmed. Interatom began work on a pipe-construction plant in the Baghdad area but halted work when the U.N. embargo against Iraq was enacted.

Interatom said it cut off deliveries of machinery that the Iraqis said were to be used in petrochemical and pharmaceutical plants after the Bonn economics ministry notified the company last April that it had reason to question Iraqi intentions.

Vogel said the government has no evidence that Interatom made illegal deliveries.

More than 100 German companies are under investigation for allegedly violating export laws by sending nuclear or other arms technology to Iraq, according to German authorities.

The German government boasts that it has the toughest penalties in the world for export violations. But export authorities have admitted that they are virtually powerless to stop companies that circumvent the Iraq embargo by sending their materials via third countries.