Civil servants who take what they can get, and postal workers who get what they can take, met briefly yesterday right smack in the middle of Independence Avenue.

There was plenty of symbolism in the "confrontation" between the two groups of government employes who have almost nothing, except the same Uncle Sam, in common.

The more docile white collar workers, who by law and tradition depend on Congress and the White House to hand out pay and fringe benefits, stood aside. They watched, from the street or air-conditioned offices, as nearly 4,000 militant mailmen and women marched on, the U.S. Postal Service's plush, futuristic building at L'Enfant Plaza.

While the white collar employes watched, some applauding, some embarrassed, some grim-faced, the postal union members chanted "no contract, no work," and threatened to shut down the mail service unless they get a substantial pay raise and lifetime job guarantees.

Joggers from the Agriculture Department, Defense agencies and AMTRAK ran by the postal people, dressed not in Adidas outfits but in rumpled clothes and well-worn walking shoes, wondering what it was all about.

What it was about, in effect, is the tremendous difference between the way white collar federal workers and military personnel view the government and are treated by it, compared to the simpler, get tough approach of the postals.

In the midst of the march, which snaked from the Washington Monument, a chauffered limousine bearing three of the president's top federal pay advisers got stuck in the traffic. The officials - from the White House, Office of Management and Budget and the Civil Service Commission, watched as the postal people berated Jimmy Carter for asking them to take "peanuts", the same 5.5 percent raise he has ordered white collar workers to settle for this year.

(At a Civil Service Commission briefing, while the march was taking place, federal officials conceded that white collar government workers are due a raise of about 8.04 percent this October. But they also noted that the president will probably be successful in keeping that raise to 5.5 percent).

The contract between the USPS and its 550,000 union workers expires July 20. The unions want a 14 percent raise (it would cost nearly $3 billion by USPS estimates), improved cost-of-living pay adjustments and a continuation of the no-layoff pledge by the USPS.

In talking with postal workers yesterday, one got the impression that while they will not settle for 5.5 percent like their white collar counterparts, money is not the real issue.

Judi Bari and Bob Banhart, who work at the gaint bulk mail center in Largo, said their 700 fellow employes are worried about the possibility of layoffs if the USPS refuses to continue the agreement not to fire workers because of installation closing or automation.

Another Largo worker, who said he has recently transferred up from Tidewater Virginia, said forced overtime and dangerous working conditions were driving employes to desperation. Employes said mandatory 60-hour work weeks are routine. They want a contract that will permit them to refuse overtime.

Bob McCeney, president of the Letter Carriers local for Northern Virginia, said his 755 members want a satisfactory contract by deadline time. McCeney said he did not think his people would engage in a wildcat walkout (a nationwide postal wildcat in 1970 idled 220,000 workers). But that he felt they would support a national strike if the union ordered it.

The demonstrators came, mainly by bus, from as far away as Iowa. Meantime, similar demonstrations were being held in other cities.

Washington, D.C., Postal Local 142 had signs saying "Jimmy, We Don't Want Your Peanuts." Delegates from Baltimore said the USPS is handling 93 billion pieces of mail a year, with 70,000 fewer employes than two years ago.

A Roanoke, Va., group of postal workers, recalling the use of Army troops during the 1970 strike, had signs which read: "If the National Guard Moves the Mail The Mail Won't Move."

Some tourists joked with the demonstrators. Some complained about the recent stamp price increase, and asked if the union's demands would again jack prices up.

A few, looking at the throng of postal employes, joked aloud, wondering "who is delivering the mail?" A union leader nearby said "that might be a good question to ask again in eight days."