Postal workers, the heavily unionized shock troops of the federal government, will probably surpass their white collar civil service brethen in the pay parade in the next couple of years.

Thanks to the new contract with the U.S. Postal Service, the pay of the typical postal clerk and letter carrier could go up $3 for every $1 increase that white collar federal workers (whose average pay is now $21,000 a year; $23,000 in metro Washington) get over the next few years.

The guaranteed postal pay raises, plus regular cost-of-living adjustments promised every six months during the life of the contract, is almost certain to push the average postal salary -- now slightly behind the regular civil service -- well ahead of the average for white collar government employes.

Eight of every 10 postal workers carry a union card. Except for Tennessee Valley Authority workers, USPS people are the only big segment of the federal workforce that bargains with the government over wages and fringe benefits. (The Professional Air Traffic Controllers Organization, by the way, besides being much smaller, was not bargaining directly with the government the way postal unions did.)

The government clearly was willing to risk a PATCO strike, but the threat of a postal strike -- illegal though it would be -- carried enough weight to get a strike-free settlement. It is one thing to fire and replace 12,000 controllers, quite another to figure out what would happen if half a million postal employes hit the bricks.

Under the new contract with the postal service -- a contract quickly ratified with the promise of a $150 bonus per person -- this is part of what the average postal employe will get over the next three years:

* A $300 salary increase this year, in 1982 and again in 1983.

* A $350 cash payment each year for 3 years.

* The $150 bonus for ratifying the contract within 45 days.

Officials of the American Postal Workers Union and National Association of Letter Carriers figure that the pay raises, annual cash payments and bonus will be worth $2,100 per member during the life of the contract.

The big item, however, is the promise of a more generous system of regular cost-of-living catch-ups that, at the current rate of inflation, will be worth at least $5,000 for each eligible employe.

Postal workers will also get extra protection from higher insurance costs that are coming for all federal and postal employes next year. Their contract provides that the USPS will pay 75 percent of the health insurance premium, whereas the government pays only 60 percent of the premium for other workers.