As the Office of Management and Budget continues to push agencies to see if some of their jobs could be performed at less expense by private contractors, it contends that federal employes now are winning as many cost comparisons as they are losing.

Under what is known as OMB Circular A-76, agencies are supposed to review every five years jobs that are not inherently governmental to see if the private sector could do them for less money.

According to OMB, 59 percent of the 34,762 Defense Department jobs that were reviewed from fiscal 1979 to 1983 were turned over to the private sector. At civilian agencies, 201 of the 287 cost-comparisons were won by private contractors.

But in fiscal 1984, OMB officials said, government employes retained as many of the functions as they lost, according to preliminary figures. At the Pentagon, 4,342 of the 8,474 jobs reviewed were turned over to contractors. And, based on the preliminary figures that OMB has collected from civilian agencies, where fewer than 2,000 jobs were at stake, the same trend appeared to be occurring there.

The cost comparisons are a sensitive subject for government workers, their unions and sympathetic members of Congress. They have watched with concern as the Reagan administration has vowed to make "management reforms" and shave the cost of running the government wherever possible.

This year the administration is stepping up its efforts. It plans to review 115,000 jobs between now and fiscal 1988, with a goal of saving an estimated $928.7 million. For the first time, most of those jobs will be in the civilian agencies where reviews traditionally have resulted in a larger percentage of jobs being won by contractors.

But OMB officials contend that employes are taking steps to increase their productivity, and thus win more of the reviews.

David S. Muzio, the senior OMB official monitoring the program, projected on the basis of last year's results that by fiscal 1987, federal employes will retain up to 70 percent of the jobs reviewed. But he acknowledged, "While we feel that productivity has improved greatly, it's a hard thing to measure."

Officials of federal employes' unions, however, are skeptical.

"We would tend to disagree with the accuracy of the OMB statistics," said David Gusky, executive director of the National Federation of Federal Employes. "But we have no statistics of our own. It's a sense based on a survey of our locals."

Bob E. Edgell, a government procurement specialist with the American Federation of Government Employes, said the administration "is simply looking for ways to reduce the size of government. Ideologically and conceptually, they are convinced that it is cost effective to turn work over to the private sector. These numbers are only being used to support increased A-76 activity."

Gusky said, "Any job that is put up for an A-76 review will likely be awarded to the private sector. They'll never reach 55 or 60 percent of the work being kept in house."

When an agency decides to try contracting out a job, its employes are supposed to be allowed to estimate what it would cost them to do it, taking into account ways they could improve the agency's operation. Their estimate is then compared with bids solicited from the private sector. If the private-sector bids are more than 10 percent below the government's estimate, the function is turned over to the low bidder.

According to Muzio's statistics, last year 94 percent of the Defense Department employes whose jobs were turned over to the private sector were placed in other Pentagon jobs. On the civilian side, he said, the figure is about 80 percent annually. Under the A-76 guidelines, contractors are supposed to give displaced federal workers the first crack at the private jobs, although the jobs often pay less and have fewer benefits.

But both Gusky and Edgell contended that the civilian placement rate was overstated. Gusky agreed that the Defense Department does a good job of placing employes, but Edgell said it was often at the expense of other, lower-level employes.

For example, he said, when the U.S. Army Tank Automotive Command in Warren, Mich., conducted a cost review, a private firm won the contract, displacing 300 employes. But, he said, more than 900 personnel actions were involved. "That's the ripple effect," he said. "Someone down the line was gone."

A group, Blacks in Government, also has kept a wary eye on the program because of its concern that most of the jobs involved are staffed by blacks in disproportionately high numbers.

Members of the group met with OMB officials last year to complain that the agency was ignoring the "humanistic aspects" of contracting out. Muzio said that sessions like those led OMB to decide last fall to target its reviews on 14 job classifications, half of them white-collar jobs and the other half blue-collar.

The OMB also is planning to rewrite the A-76 regulations this spring in response to some of the concerns. It intends to strengthen the requirements for placing affected employes in new jobs and require agencies to seek the advice of other agencies that have conducted similar reviews.

But at this point, OMB does not plan to address some of the unions' areas of greatest concern. They want to bar the use of "cost-plus contracts" in which a firm that has won a contract gets to take on new functions -- without a review -- when the government decides that other, previously unrelated jobs, also should be phased out. The unions also want to take steps that they say will make the cost comparisons more balanced.

"If a system is fair, in that it accurately measures that a job can be done less expensively and more efficiently, then we would have no argument with it," Gusky said. "But it is our contention that the system is skewed in favor of private-sector bidders. The rules need to be changed."