Prosecutors said Wednesday they have opened a criminal investigation into I.B.I. Engineering, a company U.S. officials accused of helping build a suspected Libyan chemical weapons plant.

In Bonn, opposition lawmakers shouted and hooted during a parliamentary session in which the government again altered its official position on when it knew about the suspect plant, which Libya claims will produce pharmaceuticals.Besides the I.B.I. Engineering probe, federal officials are investigating overall West German involvement, and a local prosecutor in the southern city of Offenburg is investigating the Imhausen-Chemie company. U.S. officials say Imhausen also was a major participant in the Libyan project.

West Germany's ARD television estimated that 50 companies in the Frankfurt area alone had a role in building the Libyan plant.

"Our authorities opened the probe against I.B.I. on Friday because of suspicion of reported violations of export laws," Frankfurt prosecutor Jochen Schroers told The Associated Press in a telephone interview Wednesday. He did not say why the investigation was not announced earlier.

Earlier Wednesday in Munich, prosecutors said they have begun a criminal investigation of a Bavarian firm that a news magazine says helped Libya develop the ability for in-flight refueling of warplanes.

Munich prosecutor Heinz Stocker said the Intec Technical Trade and Logistic company was suspected of violating West Germany's export laws.

He said the probe was focusing on whether "(fuel) tank equipment sent to Libya required an export permit."