Federal health inspectors and Pentagon investigators have begun a joint probe of claims by Lockheed workers that they are endangered by chemicals believed to be used in making the top-secret Stealth fighter. A three-member team from the Occupational Safety and Health Administration made a visit Thursday to the aerospace company's Burbank plant, where 75 employees have filed suit complaining they suffer from ailments brought on by exposure to hazardous substances used in their top-secret jobs. A team of military physicians, toxic material experts and other specialists from the Department of Defense are expected to be at the plant by Monday, according to an announcement Thursday by Rep. Howard Berman, D-Calif., whose district includes the Los Angeles suburb where the plant is located. In addition to the lawsuit, about 150 employees have filed worker's compensation claims related to exposure to the chemicals. The employees, some of whom work in Lockheed's highly classified plant nicknamed the ``Skunk Works,'' where the U-2 reconnaissance planes were built, have said the top-secret nature of their jobs has hampered their efforts to seek treatment from private physicians. Attorney Timothy Larson, who represents the workers in the suit and compensation claims, said five of his clients and an unknown number of workers have died since 1986. Lockheed workers claim composite materials used in the Stealth fighter, designed not to reflect radar, and chemicals used to mill or clean them are causing rashes, nausea, dizziness, memory loss and lack of concentration, Berman said. Similar symptoms have been cited in the Seattle area by workers at Boeing plants, where many of the same materials are used on commercial aircraft. In Washington, the Senate Environment and Public Works Committee wants to determine whether workers in aerospace facilities with DOD contracts are being exposed to hazardous chemicals without adequate protection. No state or federal OSHA inspector has conducted a full-scale inspection of the top-secret Skunk Works since the safety agency was founded 16 years ago, high-ranking OSHA sources told the Los Angeles Times this week. An OSHA inspector with a nuclear-materials security clearance from the Department of Energy was admitted to the secure section of the plant Thursday and will remain there for several days, an OSHA official told the Los Angeles Times. ``He will look first into the specific complaints contained in the lawsuit and media reports and after that will decide whether to expand this into a wall-to-wall general inspection,'' said the spokesman, not identified by the Times.