Much against his better judgement, the "umbrella man" turned up before the House Assassination Committee yesterday. He even brought his "stupid umbrella."

Anonymous for nearly 15 years despite his status in assassination lore, Louie Steven Witt, 53, said he was the person 22, 1963, his umbrella incongrouously aloft in the sunshine, when President Kennedy was shot.

He said he'd come to heckle the president that day, nothing more. He's been embarrassed about it ever since.

"I wish I could remember who it has who put this idea into my head." Witt testified yesterday, "I'm sure I would have taken the umbrella and clouted him with it sometime the last two or two weeks."

Seizing on pictures taken of him just a few feet from the presidential limousine when the fatal shots rang out, conspiracy theorists for years have made the "umbrella man" a sinister figure. Some suggested he was serving as a sigal man for the real assassins, opening his umbrella as a signal to begin the gunfire.

Chief committee counsel G. Robert Blakey said one critic has even contended that the umbrella may have contained an immobilizing dart gun or flechette, or even served as the murder weapon.

Witt, who at the time of the assassination worked for the Rio Grande National Life Insurance Co. in Dallas, said he'd simply been trying to annoy the president. He said a friend of his, whose name he can't remember, had told him that the umbrella was a "sore spot" with the Kennedy family ever since the president's father, Joseph P. Kennedy, had served as U.S. ambassador to Great Britain before World War II, in those days, the umbrella was the symbol of British Prime Minister Neville Chamberlain whose appeasement policy of "peace in our time" with Adolf Hitler had had Joseph Kennedy's strong support.

In any case, Witt said he'd heard that President Kennedy had been nettled on a trip to Arizona by a group of people brandishing umbrellas and he decided to try the same thing in Dallas on his lunch hour.

"I never thought too much of liberal politics in general," he explained. "The Kennedys just happened to be in office."

Now a warehouse manager for a Dallas equipment firm, Witt said he picked out the sparsely occupied grassy knoll in Dealey Plaza, sat down for a while, then got up as the motorcade began to pass.

"As I was moving forward, opening the umbrella, it was somewhere at this point that I heard the shots. . . . My view of the car was blocked by the umbrella being opened." But within moments, he said, "I was aware that something and happened."

Stunned, he sat down at the curb while the motorcade speed off. A man next to him, he recalled, kept muttering: "They done shout them folks."

Witt went back to his nearby office and kept his heckling to himself. He said that, to his knowledge, authorities never sought him out, and he never stepped forward.

"My line of thinking was I really had nothing to offer other than that I had done a foolish thing," he said.

Witt was finally forced into the limelight when Dalls newspapers published his picture as part of an effort by the House committee to determine his identity. Ruefully, Witt said he confided in a friend and the secret was soon out.

Under subpoena, he brought himself and his "big . . . clumsy" black umbrella, to Washington this week, but he declined to demonstrate for the committee what he did with it in Dallas.

Chairman Louis Stokes (D-Ohio) insisted on having it opened, to slow there was no dart gun inside. Committee staff member Cynnthia Cooper picked it up and pointed it at the chairman.

"Maybe you ought to turn it the other way," Stokes said. She did, then opened it so vigorously it turned inside, out, its metal ribs sticking up in the air. The hearing room burst into laughter, but Witt was still chiding himself for the first and only demonstration he ever took part in.

"I think if the Gunniness book of records had a category of people being in the wrong place at the wrong time doing the wrong thing," he said, "I would be No. 1."

The levity capped a day in which the committee began knocking down one conspiracy theory after another - from the idea of false Lee Harvey Oswalds to the notion that an astronomical number of a witnesses and others somehow related to the assassination died in an incredibly short length of time.

Handwriting and photographic experts said all the purported pictures and signatures of Oswald - expect for one possible forgery of an opaquely worded letter to a "Mr. Hunt." - were of the same man. The committee was also assured that the number of deaths of people supposedly related to the assassination has "no statistical significance."

The only thing the committee couldn't quite shoot down was the "man on the grassy knoll," Dr. Bob Hunt, a photo enhancement expert from the University of Arizona, said sophisticated techniques have brought out the image of an individual behind a retaining wall who may or may not have a gun in his hand.