Washington's Birthday being a truly American occasion, a friend of mine accosted me on Massachusetts Avenue early Thursday evening and politely suggested that we spend the evening observing a truly American art form. "Why don't we stomp down to the Hi-Hat and dig Illinois," he said.

He was referring to Illinois Jacquet, a saxophone player who is a popular exponent of the "wild" school. Although Jacquet has appeared at places like Symphony Hall, his music is neither classical nor modern, dixieland nor bop; it is loud.

My friend became more insistent. "Listen, Jack," he said, "the joint will really be rockin! It'll be crazy. Jacquet blows a lot of sax."

"Sure," I said.

Two hours and five drinks later we were out in the cold, coatless, in front of a squat building known as the Hi-Hat. We entered and smiled benignly at the chichat check girl. A short dapper man with horn-rimmed glasses approached us:

"Plant you somewhere?" he asked.

He led us up a flight of stairs into the main room. "The place," he said, "is really jumpin'." The concert hall of the Hi-Hat is divided into three areas: the bandstand, populated by seven bouncing musicians; a submerged central portion, filled with numerous raucous patrons; and an elevated section in the rear holding the more sedate element. The only table available was in the last section. It was partially filled and we were invited to join two young ladies at a table for six.

I don't think they noticed us when we sat down. My companion told me that Jacquet was playing "a number he waxed a while back" called Flying Home. Quick to join in the spirit of the crowd, I suggested that the music was "real gone." I must have been overheard, for one of the girls at the table glared at me and commented, "Frenetic, man, frenetic." I stood corrected.

A uniformed waitress appeared, flashing a $2 minimum card, and called for our orders. Two beers.

The evening ripped along. Two student-type males moved into a table across from us with two Wellesley type girls. Their order, two scotches and two cokes, was taken. The men lit cigars and Jeaned back while the girls beat frantically on the table. A pert female photographer saw them and invitingly addressed the leader of the repp-tied party. "How about a picture, sonny?" He picked up his drink, took a careful swallow, and consulted the group. "Sure, baby, sure," he said.

Jacquet was off on another number. This time the air was punctuated by shouts of "Go! Go!" A minute later I picked it up. My companion turned to me disdainfully. "Not now," he said, "not now."

"When?" I asked.

"Later," he said. "You only yell 'go' when the man's ending a chorus and you want him to keep driving."

"But isn't most of the stuff arranged ahead of time?" I asked.

"Yeah," he said.

"Oh."

We sat there for two hours, rockin. As we were leaving, the dapper man with the horned-rim glassed waved goodbye. "You'll float all the way home," he said. HERBERT S. MEYERS