Glenn Sinclair, a short, muscular ex-Marine, proudly served his country for nearly 13 months in Vietnam. But now he is so enraged that yesterday he stood up in a House caucus room and angrily blamed his government for the "five screwed-up kids" he has fathered since his battlefield days near the DMZ.

The source of Sinclair's wrath is Agent Orange, the toxic herbicide American forces used as a defoliant in Vietnam for 10 years. But the object of his fury is the Veterans Administration, which has become the new enemy for thousands of veterans with a variety of ailments and deformed children.

Hundreds of veterans who came to Washington this week to pay tribute to their fallen comrades and view the new Vietnam Veterans Memorial are also taking the opportunity to vocally express their displeasure at what they see as the inept, uncaring manner the VA has exhibited in dealing with the after-effects of Agent Orange.

About 300 people attended the Capitol Hill forum on Agent Orange sponsored by the Vietnam Veterans of America and the estimated 200 veterans in the audience cheered and applauded lustily as veteran after veteran cited their medical problems or those of their offspring.

Grim-faced Veterans Administration officials did not attempt to respond to specific complaints about the care VA hospitals are providing, but instead repeatedly stated their commitment to finding out whether Agent Orange indeed causes all the ailments, diseases and disorders that veterans suspect it does.

The VA officially recognizes only that the poisonous dioxin in Agent Orange causes chloracne, a skin rash, and says it has treated more than 900 veterans for the ailment.

But medical science has yet to prove that it causes anything else, the crowd was told by Dr. Barclay Shepard, the acting director of the VA's Agent Orange office. He said it would be "another three or four years before we have a significant body of evidence."

The veterans, however, pointed to a host of other unexplained medical problems they are experiencing and demanded answers from the VA officials. In addition to the chloracne, veterans say the defoliant has variously caused cancers, nerve, liver and kidney disorders, tingling in their fingers, numbness, vision and hearing impairments, fatigue, reduced sexual drive, impotence, miscarriages in their wives and birth defects in their children.

Sinclair, his reddening face quivering as he choked back tears, charged that in his dealings with the VA, "You treated me like dirt and we're sick of it."

He said Agent Orange was pervasive for the Americans who served in Vietnam during the period in which the defoliant was sprayed on wide swaths of the countryside -- from 1962 to 1971, when its use was discontinued after someone noticed that Vietnamese women were giving birth to a large number of deformed babies.

"We lived with it, we slept with it, we bathed in it," shouted Sinclair, a 35-year-old electrician for the Cleveland school system.

"We don't want money," he said. "We want an admission that they did this to us over there. We don't trust you!"

Sinclair's remark drew long and boisterous applause from the veterans in the room, many of them wearing fatigue jackets emblazoned with unit patches and ribbons from the war.

"We'll work through the system, but you're going to have to answer," Sinclair pointedly told Shepard.

Sinclair later told reporters that his wife suffered a miscarriage in her first pregnancy. Now, he said, his son Jeffrey, 12, has unexplained spots on his lungs; his daughter Jennifer, 10, and son Jonathan, 4, have immunological problems; his son Jason, 7, has a brain defect, and his son James, 1, was born with three kidneys, two of which did not work.

Consequently, he said, he has concluded that Agent Orange caused the deformities.

Dr. Donald Custis, the VA's chief medical director, sat in the front row of the audience and listened to the outbursts of Sinclair and other veterans and then reminded the crowd that he, too, had been exposed to Agent Orange when he served in Vietnam.

"I came here to listen," he said. "I've heard you and I've heard you loud and clear. I don't come to offer any excuses, because I'm sure in many cases we've fallen short. We're going to keep trying."

Congress ordered the VA three years ago to undertake a study of the health effects of Agent Orange. But the agency has been unable to decide on how to proceed with the study and now is negotiating with the Centers for Disease Control to take over the investigation.

The result is that many veterans do not think the VA takes their problems seriously, a problem that was exacerbated when Robert P. Nimmo, who has announced his resignation as VA chief, once compared the effects of Agent Orange to teen-age acne.

Marine Cpl. Phillip Smith, 31, of Las Vegas, is one of many GIs who have filed suit against the manufacturers of Agent Orange. He lost both legs in a Vietcong ambush in 1970 and said he gets red lumps the size of golf balls on the stump of his left leg that VA doctors have been unable to explain.

Smith, who now is wheelchair-bound because he can no longer wear artificial legs because of the lumps, thinks he knows the reason: Agent Orange.

Smith's friend, onetime Marine Cpl. George Porter, 37, blames Agent Orange as well for the frequent illnesses his son Jonathan suffers and his own hearing loss, ulcers, boil-like lumps on his back and diminished sexual drive.

He remembers the Agent Orange spraying missions when he was stationed near a place the Marines called the Rock Pile.

"They flew right over our position and dumped it," he recalled. "I don't think they knew what the effects would be."