To the Editor:

Rick Marin's Sept. 12 column on the partygiver Liz Cohen, ''The Hostess With the Most (Best Friends),'' contained a word-combo that Walter Winchell, Mr. Marin's decades-removed predecessor as chronicler of the Manhattan social and underworld scene, would have been proud to appropriate. As my old friend Agnes DeMille would have said, ''celebutante'' is ''delicious.'' But Rick, you've got to brush up on your spelling. It's not ''mega-superflak,'' it's ''mega-superflack.''

''Flak'' is short for the German antiaircraft gun of World War II that brought down so many American planes. G.I.'s adapted flak as the term for the shells fired at their planes. ''Flack'' originated in the 1930's when Variety started using it as a sort of homage to Gene Flack, an energetic movie publicist.

''To flack'' means to promote. It's generic now, and its use often raises the hackles of some public relations practitioners who consider it demeaning. I've never felt insulted when the term has been applied to me. Indeed, I've taken it as a compliment. Gene Flack was very good at what he did.

WES PEDERSEN

Washington

The writer is the communications director of the Public Affairs Council, a professional organization.