A U.S. senator rattled a sedate conference on defense issues here Saturday when he accused the West German government of failing to stop equipment supplies from being shipped to a suspected chemical weapons plant in Libya.

Sen. John S. McCain III, R-Ariz., told the high-level seminar that senior Bonn officials "must have known that West German firms were contributing to the proliferation of chemical and biological weapons."Let me be blunt," continued the senator, a former Navy combat pilot and prisoner of war in North Vietnam: "I know that the West German government is denying what was going on in Libya - and that its foreign minister is claiming to be shocked by what has happened.

"It seems increasingly apparent that the West German government first denied what it already knew to be the truth and that it has known for half a decade that West German companies have been assisting nations like Iraq to produce their chemical weapons."

"Is it conceivable that the foreign minister of West Germany could really be shocked by what happened in Libya?" McCain asked.

"Is it conceivable that the United States intelligence data that was then provided to West Germany did not reach the foreign minster?

"Is it conceivable that the West German government really made the efforts it promised to make to investigate what was happening to halt such proliferation?"

McCain's accusations, delivered in serious, measured tones, were highly unusual in light of the fudged diplomatic jargon that usually accompanies such conferences among Western allies.

The senator's plea to halt the spread of chemical and biological weapons came after an earlier speech by West German Defense Minister Rupert Scholz to the 26th annual Wehrkunde conference, a private defense seminar.

Scholz skirted the sensitive issue of aid to chemical weapons plants and the question among NATO allies about whether Chancellor Helmut Kohl's government will approve proposed modernization of the so-called tactical, or short-range, nuclear missiles that are part of the North Atlantic Treaty Organization's arsenal.

But Scholz warned Americans that if they keep complaining that Europeans are not doing their part in "burden-sharing" for common defense, it could have a negative reaction on the continent.

"The transfer of the problems the United States experiences in its financial and budget policies to Europe," the defense minister said, "could at long last drive the Europeans to feel reluctance vis-a-vis their commitments within the alliance and indignation against their American ally.

"The American-European relationship comes under a strain in such a climate," he added.

Later, in a reply to McCain, Scholz insisted that he, Kohl and Foreign Minister Hans-Dietrich Genscher were not told about U.S. information that West German industries were contributing to the suspected Libyan chemical arms project until their visit to Washington last November.

The information, Scholz said, "was completely new. It was obviously a shock to all of us." Scholz added that McCain's remarks about Genscher were "not very fair."

Yet Scholz's defense contradicted the Bonn government's own earlier version of the controversial events. In an official report to the Bundestag (Parliament), Kohl's chief-of-staff, Wolfgang Schaeuble, had admitted that Washington passed along information to the West German government months earlier.

Political observers said that Scholz's remarks will serve only to further confuse the Libyan chemical plant scandal. The question, what did Kohl know and when did he know it, has burgeoned into the most serious crisis in his 61/2 years of government.

When U.S. charges first surfaced that West German companies helped in the design and construction of a suspected poison gas plant at Rabta, southwest of the Libyan capital of Tripoli, Bonn denied any involvement by the country's companies.

The official story changed two or three times, as new material was uncovered by the media here, indicating that West German companies knowingly helped the Libyan project and had earlier done the same in the case of a poison gas factory in Iraq.

McCain's remarks shook up the normally clubby atmosphere of the defense conference. The senator said that proliferation of chemical weapons is an "issue of the utmost gravity" that represents a "major challenge to the Western Alliance and the world."

"We cannot sit by and rely on conventional diplomacy to solve these problems," he said.