LOS ALAMOS, N.M. (AP) - With firefighters holding their ground against the largest wildfire ever in New Mexico, officials at the nation's premier nuclear weapons laboratory and in the surrounding city planned for the return of thousands of evacuated employees and residents.

The blaze was several miles upslope Saturday from Los Alamos National Laboratory, boosting confidence that it no longer posed an immediate threat to the facility.

Thousands of experiments, including those on two supercomputers and studies on extending the life of 1960s-era nuclear bombs, have been put on hold because of the fire. Hundreds of employees began returning to the lab Saturday to begin the process of getting things ready for scientists, technicians and other employees to return to work.

Employees were checking filters in air handling systems to ensure they weren't affected by smoke from the fire, utilities were operational, as well as restarting computer systems shutdown when the lab closed.

"Once we start operation phases for the laboratory, it will take about two days to bring everyone back and have the laboratory fully operations," Lab Director Charles McMillan said. "I'd like to continue to ask the employees of the laboratory to continue to be patient."

Authorities didn't give a timetable for when they would lift evacuation order that began Monday for the town of Los Alamos, home to 12,000 people.

But some county workers were already back to prepare for the eventual rush of utility service calls, as well as possible flooding from surrounding mountainsides denuded by the wildfire.

Fire officials were sure the fire wouldn't spread into the lab along its north and west boundaries.

While they are confident the fire won't spread down Los Alamos Canyon and into the town and parts of the lab, firefighters were planning on burning out grasses and shrubs along the western edge of Los Alamos even though that area burned in 2000.

That the fire is burning in areas west of Los Alamos and in Santa Clara Canyon, north of town, that the Native American tribe there holds sacred, is an indication of how severe the fire danger is in the southwest. Burn areas typically provide spots to help stop fires.