WASHINGTON (AP) _ One White House guest took off her high heels and tiptoed through the mud to her table. Other guests looked warily at the tented ceiling, which was billowing in high wind and a torrential downpour.

''Welcome to Woodstock,'' joked blues singer Patti Austin as she greeted 1,000 composers and writers Thursday night on the soggy South Lawn of the White House.

Eight rhythm and blues singers and musical groups entertained until past midnight. Though the music was fine, people in the audience didn't tap their feet; they squished them.

''We're a little wet, but I hope you're as glad to be here as Hillary and I are,'' declared President Clinton, who along with Mrs. Clinton, made his way down a center aisle that had been covered with boards so the first couple wouldn't have to get down in the mud.

An entire day of rain soaked the grass beneath the huge tent erected for the evening - a celebration of American music that was a greeting to the International Confederation of Societies of Authors and Composers.

Confederation members are holding their 39th World Congress.

Other performers: rhythm and blues artist Ruth Brown; Booker T & the MG's, originators of the mid-'60s rhythm and blues style that became known as ''The Memphis Sound''; the Pointer Sisters; vocalist and songwriter Michael Bolton, a two-time Grammy award winner; and Nickolas Ashford and Valerie Simpson, rhythm and blues' most notable husband and wife songwriting and recording team. Also performing were jazz musician John Hendricks and Lyle Lovett, a songwriter and recording artist whose work runs from the blues to jazz to country and western.