WE HAVE on many occasions extolled the virtues of regional cooperation between the many local governments in Greater Washington, but last week such cooperation paid off in pure political clout. This time it wasn't a matter brought up after expert research and evaluation for the considered judgment of the Metropolitan Washington Council of Governments. What happened was a threat from the feds: news of a proposal to close the Washington field office of the U.S. Department of Housing and Urban Development. Now, before you dismiss this as an inside- the-bureaucracy tempest, here's what was a stake, at least as regional officials saw it:

The possible loss of big money, in the form of federal housing grants for the region. The field office, located in downtown Washington, administers federal housing programs for the metropolitan area. Local officials feared that a breakup of the office would mean less access to dwindling federal monies. Without this office, Northern Virginia would have to compete with other areas of Virginia for money flowing through Richmond; suburban Maryland would have to compete with Baltimore in that city's office.

Worst of all, the District might have had to deal with three separate HUD offices -- Philadelphia for public housing, Baltimore for other multifamily housing programs and a smaller office in Southwest Washington for single-family housing programs.

D.C. council member H. R. Crawford, who is chairman of COG, says he knew that a protest from the District government, or from Fairfax County or from Prince George's could easily be ignored. But together -- as a regional group -- a strong protest might have some weight. A letter went out to HUD Secretary Samuel R. Pierce Jr., noting that the region regarded the proposed reorganization "as a serious attack on housing and community deelopment programs and planning efforts in the Washington metropolitan area."

Mr. Crawford then teamed up with Fairfax County Supervisor Martha V. Pennino and Takoma Park Mayor Sammie A. Abbott for a press conference to denounce the plan. They noted that it would break up cooperation among the Washington area jurisdictions to deal with housing on a sensible metropolitan basis.

Bingo. A day later, HUD announced that the plan to close the office was dead, that the estimated savings, if any, would not warrant the move. "This," said Mr. Crawford with satisfaction, "is what COG is all about now."