Richard S. Williamson is giving up the care and feeding of governors, mayors, county commissioners and state legislators--the salt of the earth, as everyone knows--to be the U.S. ambassador to the international agencies headquartered in Vienna.

Williamson, who is only 33 and therefore can be forgiven his folly, is actually abandoning his position as the assistant to the president for intergovernmental relations and leaving the center of power on the Potomac for a backwater burg on the Blue Danube.

To be sure, Vienna offers operas, beautiful women and rich desserts --in any order and any quantity you wish. But there hasn't been a lively discussion of federalism in any of the Vienna coffeehouses since the dissolution of the Hapsburg Empire.

And federalism is Rich Williamson's abiding passion--or so he led us to believe during these last 27 months, when he, more than anyone else in the White House, nurtured President Reagan's dream of handing off some of Washington's power and responsibility to the state and local governments of the land.

The dream, as you may have noticed, has not become a reality. But that is not for lack of Williamson's trying. He has negotiated and explained, coaxed and cajoled, until he is blue in the face--and the great federalism initiative is about where it was when Reagan came to office.

There have been some consolidations of categorical aid programs into block grants, but the blockbuster plan unveiled by Reagan in his 1982 State of the Union address, a grandiose swap and turnback package involving major welfare and health programs, died aborning. Williamson was never able to bridge the differences within the administration and between the administration and the nation's governors and mayors on how the scheme would work.

So Williamson had a "learning experience," probably more valuable than his brief stewardship as manager of Rep. Philip M. Crane's (R-Ill.) abortive bid for the 1980 presidential nomination, but not much more of a success. What commands admiration, though, is the doggedness of his advocacy. If I were a defendant with a really weak case, I'd want Williamson as my lawyer.

On his way out the door, so to speak, Williamson has written a short essay for American Education magazine, summarizing the reasons that make federalism a cause of enduring importance--at least in the eyes of us true believers. His propositions are simple and significant: "Federalism fosters social harmony because it reduces government to a manageable scale and makes citizen participation more readily accessible. . . . Federalism promotes civic responsibility by fostering citizen participation. . . . Federalism helps secure individual rights by providing multiple avenues of redress. . . .

"Federalism provides diversity and allows for local considerations in problem solving. . . . Federalism fosters accountability because state and local officials are more accessible to the people. . . . Federalism is efficient because responsibilities are sorted out. With a national government focusing on national problems, and state and local governments handling their own local problems, the system does not become overloaded and congested."

Those principles are sound. Because they are, the "sorting out" of which Williamson speaks must remain on the agenda for some future president to tackle. But it won't happen this year. Federalism is "on the back burner," as Utah Gov. Scott Matheson, chairman of the National Governors Association, put it, subordinated to the budget battle and economic and foreign policy concerns.

The "jobs program" Congress passed and Reagan signed last month is largely an old-fashioned federal program, with little role for the states. An effort to help local governments offset the revenue losses of the recession by advancing their revenue-sharing payment date passed the Senate, as part of the "jobs" bill, but was killed in the House-Senate conference.

In short, the president and Congress once again have been diverted from the arduous task of "sorting out" the functions of federal, state and local governments, and once again are behaving as if all of the responsibility had to be focused here.

That means some future Rich Williamson will have to take up the cudgels for federalism in the second Reagan term--or in somebody else's White House.

Meantime, Williamson has nothing but Strauss and strudel to console him. Poor fellow. All us federalists envy him his bad luck.