Contractors seeking a bigger chunk of the Pentagon dollar are pushing Defense managers to sign on the dotted line before Congress slaps a freeze on any new personal-service contract deals.

The freeze - when and if it comes - could alter Defense plans to lay off civilian federal employees whose work is tentatively slated to go to contractors who say they can deliver more services for less money.

Federal employee unions have been fighting the trend toward increased contracting out. They contend that it has cost thousands of civil service jobs and inflated the Defense budget. Under both Presidents Ford and Nixon, the military services - and other federal agencies - increased the number of government services that are handled by private industry.

Estimates of the amount of work the government now contracts out vary, ranging from a low of $6 billion to a high of more than double that amount.

The private firms that supply serivces to Defense - ranging from cooking and maintenance to running telephone switchboards and supplying security guards - got a jolt last week from the House Armed Services Committee.

The committee voted, in effect, to freeze all new Defense contracting-out of personal services until Congress and the Pentagon could get new estimates of the cost of having work done in house, by government workers, as opposed to letting industry handle it.

When in-house proponents do the arithmetic, private industry comes out looking like modern-day pirates, dragging out work and soaking the taxpayers by delivering inferior performance. When industry does the calculating government workers appear to be permanently entrenched drones who do little more than draw big salaries and benefits with none of the responsiveness of industry.

The Armed Services Committee wants an independent source - if there is such a thing - to come up with guidelines to help the committee and Defense determine whether civil servants or private employees can do the work more efficiently.

Meantime, Chairman George H. Mahon (D-Tex.) has written Defense Secretary Harold Brown, advising him to go slow in converting in-house government services to commercial contract. Coming from Mahon, who controls the Defense-money spigot, the letter has the effect of a howitzer being fired down the C ring corridors of the Pentagon.

Mahon said the Pentagon may be rushing ahead with plans to convert more civil service work to private contract.

"The committee has had many years of experience with efforts to convert in-house government services to commercial contract," Mahos wrote Brown. "We have found such efforts to generally lead to higher costs, needless confusion and consternation on the part of government personnel, poorer management since contract employees are not as closely supervised as government employees, and a gerneral deterioration of services. . ."

Carter adminstration officals, anxious to minimize the already growing friction between Congress and the White House, believe for the moment that they should slow the contracting pace. The impact of this - and of the pending freeze in Defense - could reduce contracting all oner government, at least for the time being.