WASHINGTON -- As many as 500 Yucca Mountain workers will receive warnings next week that they might be laid off at the end of September as part of an ongoing reorganization of the nuclear waste repository program, officials said Friday.

Notices are being prepared for about a fourth of the work force of managing contractor Bechtel SAIC and for its commercial and federal laboratory subcontractors, Bechtel spokesman Jason Bohne said.

Many of the employees affected are well-trained scientists, engineers, computer modelers and technical workers. Some of the workers are expected to be retained by Bechtel as it repositions its work plans, Bohne said.

Others are expected to be offered jobs by the Sandia National Laboratories, which is taking over portions of the Yucca project from Bechtel.

But others might not be retained. On Friday, Bohne and Sandia representative Kate Rivera said they did not know how many workers might be offered new jobs and how many might face layoffs in the fall.

"These are individuals with experience and qualifications on the project," said Rivera, manager of organizational assurance and operations for Sandia. "It's a wonderful opportunity for Sandia to tap into that talent, and we are trying to facilitate the transition as best as possible."

The Energy Department announced the reorganization in January, saying it expected the transition to be complete by October.

Sandia has been involved in DOE activities at Yucca Mountain since work began there in the early 1980s. Sandia's role is expanding to assume control of science and technical components, including projections of how long the underground repository might prevent residue of highly radioactive and decaying nuclear waste from escaping into the environment.

Bechtel is refocusing on designing above-ground facilities where nuclear waste will be transferred from trucks or rail cars and managed for emplacement.

DOE managers said the reorganization was designed to improve the project's credibility with scientists and regulators. Sandia performed a similar role in coordinating the Waste Isolation Pilot Project in Carlsbad, N.M., a repository that began receiving transuranic nuclear waste for disposal in 1999.

A job fair where Yucca employees can meet with Sandia officials and subcontractors has been scheduled for July 21 and July 22 at the Desert Vista Community Center in Summerlin, Rivera said.

Additionally, Sandia will establish a job recruitment Web site, Rivera said.

Bohne said 100 Bechtel employees and 400 subcontractor and federal laboratory workers will receive Worker Adjustment and Retraining Notification Act (WARN) notices required by federal law.

Bechtel will "send notices to everyone who could be affected and then there is a management process to identify what work scope remains and what skills we need to do that scope, and then evaluate the people we have and the skills we need to keep," Bohne said.

The total contractor work force is about 1,900, Bohne said. That includes 1,300 Bechtel employees, 300 subcontractor workers and 355 federal laboratory contractors.