Uncle Sam's pink slips have been landing on the desks of federal workers all summer. And unless the government is as zealous at finding new jobs for these employes as it has been RIFing them, thousands could be out of work by the end of next month.

That's where Reginald Jones and his staff at the Office of Personnel Management come in. It's their job to help find jobs.

"This is the time for active placement efforts," said Jones, who heads a special 16-member RIF (reduction in force) Task Force set up by OPM to coordinate and supervise the government's job hunting activities on behalf of its displaced workers.

Reducing the size of the federal government is central to President Reagan's economic recovery program. The budget cuts he has engineered have put between 9,000 to 21,000 workers -- and the numbers vary at this point -- on notice that their jobs are in jeopardy.

It is expected, according to OPM and congressional estimates, that 4,600 to 16,000 federal employes will be "separated" from government service by the close of fiscal 1981 on Sept. 30. In the Washington area, more than 4,200 workers could lose their jobs.

"We're getting down to those last few days before an agency can issue RIF notices and still give their employes the required 30-day notice," Jones said in an interview this week. "Aug. 30 is it."

Of course, he added, several agencies sent out general RIF alert notices to all employes in anticipation of ordering some lay-offs. That way, when managers finally figure out who is to go and who is to stay, final dismissal notices may come as late as five days before the Sept. 30 deadline.

"That's why the numbers sort of shimmer in front of your eyes," said Jones, explaining why estimates of job losses have shifted and varied so widely. Some agencies announced RIF plans, then later scaled them back or canceled them. Other departments held off RIF preparations until the last minute.

The agencies that will be hit hardest by Reagan's budget and program reductions ar the Community Services Administration, which is being abolished, the Department of Health and Human Services, where 13,000 Public Health Service employes have received RIF notices, the Agriculture Department's Federal Grain Inspection Service, the Department of Energy and the Interior Department.

"There were some agencies that didn't believe it was going to happen," said Jones. "They thought they would get bailed out."

But it is happening, and the OPM task force is busily cranking up its job assistance programs. They are working with all government agencies and the private sector, encouraging everyone to be on the look-out for vacancies that could be filled by displaced federal workers.

"I normally do a totally different job," said Jones, 47, OPM's assistant director of natural resources, energy and science agency relations. He and aides like Ron Redmon, Susan McConnell and Barbara Powers have been borrowed from other OPM offices to oversee government-wide placement services. They work with job counselors in each of the agencies to find jobs for individual workers.

To this end, there is the Reagan-endorsed voluntary interagency placement program (VIPP) where agencies can register workers who face the prospect of losing their jobs. OPM keeps a computerized job referral matching system that lists agency vacancies and job openings in the private sector and with state and local governments in each of its 10 regions.

So far, the VIPP program, set up in June, has resulted in 270 placements in the regions and six placements in the Washington area. More than 1,000 area workers have been referred to private and public sector jobs here, and OPM officials are expecting the placements to pick up soon. The majority of the 276 workers placed so far found their new jobs with the federal government.

There is also a displaced employes program, a government-wide referral for workers who have received RIF notices and can't be placed within their agencies, either because their agency is being abolished or there is no available job for a person with their skills. A positive placement program makes referral for jobs outside a worker's commuting area. And, nationally, the Labor Department is operating the federal employes reemployment registry, a pilot program that maintains a computerized list of private sector and federal jobs available around the country.

"We don't know which of these programs alone or together is going to do the trick," said Jones, who confesses that no one on the task force "has ever run a RIF before." The point, he said, is to offer as much job referral and placement assistance as possible now, while the need is so critical.

He notes that the success of OPM's efforts during what his staff considers "a test year" will determine how it repsonds to the new round of government lay-offs already being planned for next year.