At least two companies hired by the Energy Department as independent investigators of environmental and safety conditions at nuclear weapons plants are on the payroll at facilities they investigated, government records show. Others participating in the audits had bid for Energy Department contracts at sites they investigated, although they were not yet working there. Still others, while not associated with the plants they audited, are the Energy Department's prime contractors at other nuclear bomb factories. Written department guidelines for carrying out the ``independent tiger team'' investigations include a provision aimed at avoiding organizational conflicts of interest. It defines such a conflict as a situation in which a contractor ``has past, present or currently planned interests that either directly or indirectly ... may relate to the work to be performed'' and which may bias its judgment. The tiger teams were assembled by Energy Secretary James D. Watkins last summer to give an independent view of the plants' compliance with state and federal environmental, safety and health standards. The auditing work is meant to lay the groundwork for actions to correct unsafe and illegal practices at the plants. Virtually all 17 major weapons facilities have severe environmental problems; estimates of the cost of cleaning up production wastes are as high as $100 billion. Watkins publicly stressed the independence of the tiger teams but did not explain that many of the experts would be tied to the weapons business. The Energy Department, which owns the plants, declined to comment on whether the contractors' connections to the weapons industry amount to a conflict of interest that undermines the independence of the investigations or taints the findings. Department spokeswoman Catherine Kaliniak said the department would prefer to use its own employees for this work, ``but we don't have the people to do it.'' Each team is headed by a small number of department officials, but most of the scientific work is done by contract employees. Most have extensive backgrounds in nuclear environmental and safety matters. A review of department records as well as interviews with government and industry officials show that of the eight weapons plant investigations done last year, at least three involved companies that held other Energy Department contracts at the same sites or were bidding for contract work at those facilities. _The engineering and environmental consulting firm NUS Corp. of Gaithersburg, Md., was on the tiger team that investigated the Y-12 uranium processing plant at Oak Ridge, Tenn., last fall. According to department records, NUS at the same time was working for the Oak Ridge reservation on an environmental study of its nuclear and hazardous waste management. The Y-12 plant is one of several operations at the Oak Ridge reservation. NUS's Oak Ridge contract was awarded Nov. 8, 1988, and was valued at $1.4 million. The firm also holds contracts at weapons facilities in South Carolina and Idaho. NUS spokesman Don Couchman declined to discuss any aspect of the firm's work for the Energy Department. _Science Applications International Corp. of La Jolla, Calif., helped evaluate the Nevada Test Site, which conducts underground nuclear weapons tests. The company at the same time was working at the site under two Energy Department contracts with a combined value of $100 million. Most of its work is at a proposed high-level nuclear waste dump at the site that was not part of the tiger team audit. _ICF Kaiser Engineers, an engineering and construction company based in Oakland, Calif., participated in tiger team audits at the Nevada Test Site. ICF held no Energy Department contracts at the test site at the time of the investigation last November, but it was bidding for a $5 million job to help the facility's prime contractor, Reynolds Electrical & Engineering Co., Inc., develop and carry out an environmental cleanup program there. ICF Kaiser announced it won the contract 10 days after the on-site tiger team work ended Dec. 1. Similarly, records show the company participated in tiger team investigations at the Fernald uranium processing plant in Ohio and the Y-12 Oak Ridge plant while it was a bidder for major Energy Department contracts at both sites. The contract at Oak Ridge is valued at $505 million over five years, according to Bob Lynch, deputy director of the department's field office there. Marc Tipermas, executive vice president of ICF, said in a telephone interview that he saw no conflict of interest in his company's involvement in the tiger team work. He said he was not sure whether, in choosing ICF for the work, the department knew or cared about the company's other work at the weapons plants. ``In order to get this job done well and quickly, contractors had to be used,'' Tipermas said. ``Like many other companies, we were drafted. We were helter-skelter pulled onto these teams.'' The Energy Department has used private contractors to run the nuclear weapons plants since they were built as part of the World War II Manhattan Project that produced the atomic bombs dropped on Japan in 1945. The contracting system has left the department with little internal expertise in this area and a tendency to rely on the weapons makers to police themselves. Watkins strongly advocates hiring more federal employees with environmental, safety and health expertise to lessen the dependence on private contractors. Although the department insists that the tiger team members' links to the weapons industry do not compromise their objectivity as judges of environmental and safety conditions at the plants, some outside experts disagree. ``It's inevitably a potential conflict when a contractor is reviewing another contractor, and the reason is that any possible criticism of one contractor might lead to future business for another contractor,'' said Donald F. Kettl, a political science professor at Vanderbilt University and author of a book on government use of contractors. Other tiger team members included companies in charge of running nuclear weapons plants, though not the ones they investigated. These include EG&G Inc., which is the prime contractor at the Rocky Flats plutonium processing plant near Denver, the Idaho National Engineering Laboratory at Idaho Falls, which processes naval nuclear fuels, and the Mound Laboratory near Dayton, Ohio, which makes detonators for nuclear arms. Martin Marietta Energy Systems Inc., which runs the Oak Ridge facilities, participated in some other audits, as did subsidiaries of Westinghouse Electric Corp., which runs several weapons sites, and Mason and Hangar Silas Mason Co., operator of the Pantex final weapons assembly plant near Amarillo, Texas.