COLUMBIA — Three companies that employ thousands at the Savannah River Site, a nuclear cleanup complex, announced Monday that they would offer buyouts to hundreds of employees before implementing layoffs later this year.

The cuts come two years after the complex near Aiken received $1.6 billion in federal stimulus cash to create or save more than 3,000 jobs at the site, which once produced plutonium and tritium for atomic bombs but now is focused primarily on research and cleaning up areas contaminated during weapons production.

Officials with Savannah River Remediation and Wackenhut Services Inc., which provides security for the site, said they each planned to offer employees the opportunity to first leave their jobs voluntarily this spring.

Savannah River Nuclear Solutions, which managers overall operations at the 310-square-mile complex, did not say Monday how many additional employees it planned to cut. The contractor that last year employed more than 6,000 people at SRS said in November it planned to lay off 1,400 contractors this year, 800 of whom were funded with the company’s share of the federal stimulus funding.

In memos to employees, officials with each of the three contractors said they would begin offering buyouts this week, with workers who accept the packages working their last days in June or July.

“I encourage you to avoid the distractions that these workforce changes can cause,” Savannah River Remediation president Dave Olsen wrote to his employees. “I ask that you continue to focus on your jobs, particularly paying attention to the continued safe performance of all tasks.”

Funding for whatever stimulus-funded jobs that remain after the layoffs is set to run out by the end of September. While fielding thousands of applications at job fairs statewide, officials were quick to say that those jobs were only temporary and would likely expire once the time-limited funds ran out. The jobs ranged from procurement and public relations to work doing construction and general maintenance.

Residents of surrounding counties — typically home to some of the highest jobless rates in South Carolina, which posted statewide unemployment of 11 percent in September — were happy for a shot at even short-term employment. Local officials cheered the burst of economic steam generated by the $1.6 billion influx of cash, and businesses such as restaurants and gas stations along the highway leading to the site’s main gate tallied brisk business.

In April, officials with the U.S. Department of Energy, which runs the Savannah River Site, said no further layoffs would be necessary to accommodate restructuring plans. A spokesman did not immediately respond Monday to the new layoff announcements.