A congressman from Hawaii who had a $100 bill snatched from his hand in an all-night drugstore in downtown Washington over the weekend heaved a handy item at the fleeing thief.

But the missile missed its mark and struck another customer, whose aggrieved husband thereupon planted a punch in the lawmaker's face.

Rep. Cecil Heftel, a Democrat serving his third term on Capitol Hill, became embroiled early Saturday in the brief, hectic incident played out in the People's drugstore on Thomas Circle NW.

It began, according to police reports, about 12:30 a.m. when the 57-year-old congressman was standing in the store's checkout line, about to make a purchase with a $100 bill which he held in plain view.

The sight apparently proved tempting to a bystander, who, according to police accounts, approached the congressman, plucked the bill from his hand and headed for the door.

Responding quickly, the legislator reached behind the counter, seized some object -- the precise nature of which has not yet been disclosed -- and hurled it at the fast-departing holder of his $100 bill.

But, police said, the thief ducked. Accidentally struck instead, they reported, was a woman customer who was standing in the store near the congressman. The woman's husband was nearby and he, in the words of a police report, "took umbrage." This, according to the police, he made clear by proceeding to punch the congressman in the face.

Heftel went down behind the store counter. When authorities arrived, according to accounts, he was the only one of the principals who remained on the scene.

There were no charges, no arrests and no $100 bill.

After the arrival of officers from the third district of the D.C. police and from the U.S. Capitol police, Heftel was taken to Walter Reed Army Hospital for observation. He was still there last night, but could not be reached for comment.

An aide in the congressman's Capitol Hill office said last night that Heftel had been "mugged", but could provide no details.

Police said they would like to find and talk to the woman struck by the thrown object and to her husband. They said they are also seeking the man who took Heftel's $100 bill.

Heftel, a resident of Honolulu, is the president of a broadcasting company who was first elected to Congress in 1976. CAPTION: Picture, REP. CECIL HEFTEL . . . robbed of $100 bill.