The House Post Office-Civil Service Committee hopes to get into the act before Congress finally votes to put federal workers under mandatory Social Security coverage.

In the process, the committee may be able to erase some of the question marks raised by the pension linkage plans - and also to save itself from becoming a congressional merger victim next year.

Congress, at least on the House side, appears determined to extend "universal coverage" under Social Security to U.S. civil servants and postal employees who now have their own and better - retirement plan.

Although details have not been worked out, it appears that integrating the two systems would mean dual (but not double) payments would be required of federal workers. On retirement they would get two (but again, not double) benefit checks, one from Social Security and another from their own civil service retirement fund.

But in its drive to extend universal coverage to 7 million federal, state and local government workers, the Ways and Means Committe has left many questions unanswered. Among them, how do you interface two totally different systems, how do people pay for those benefits and how do they finally get benefits? And how much? And when?

The federal civil service retirement plan is much better than Social Security, paying the average retiree about three times what individuals get under Social Security. Federal workers pay more for the benefits they get, pay taxes on their pensions (Social Security is not taxable) and can retire earlier than most workers. How do you mesh those systems?

The Ways and Means Committee has directed Health, Education and Welfare, which already administers Social Security to come up with a how-to plan by 1980, two years before universal coverage would go into effect. The Civil Service Commission has been assigned a very junior-partner role in the study.

In effect the Ways and Means Committee has said what it wants done - universal coverage - but has not given clear guidance as to how it is to be done, or even if it can be done. Enter the Post Office-Civil Service Committee.

That Committee, better than any other, knows the federal fringe benefit system. As committees tend to do, it identifies with its constituient group - in this case, federal and postal workers.

Committee members are anxious to get into the complicated pension merger plan, partly to protect the interests of unions that frequently are kind to them, and also to protect their congressional turf.

Civil service pension matters, until Ways and Means reared its all-powerful head, were part of that committee's empire, which has been shrinking since Congress gave up setting federal pay raise and running the postal service. Now there is a chance to hang on to some of its legislative territory, and also to help the committee survive as a full committee with important jobs and seniority benefits for members.

There will be a "reform" drive in the House next year. It will probably be aimed at abolishing the two committees that make the least sense in Des Moines and Walla Walla - the District Committee and the Post Office-Civil Service Committee.

he Post Office-Civil Service Committee has two things going for it in any reform. Both of them are Chairman Robert N. C. Nix (D-Pa.). Nix is a strong, assertive leader who has given the committee new drive and assignments. And he is black. And he is one of only two black chairmen of major committees in Congress. Democratic House reformers are not about to knock off the only two committees that have black chairmen. And if Nix can build a bigger constituency - and the U.S. Government is bigger than the District - he will have a better chance of holding his committee intact.

Nix already is respected and popular with federal and postal unions who speak for a lot of people. If he can please them and make some sense out of the touchy question of interfacing Social Security with the civil service retirement system, he could win many more influential friends, make a lot of confused taxpayers happy and possiby preserve his committee.