A congressional committee has stopped the Veterans Administration from quietly scuttling a study of identical twins that it once said was vital to its Agent Orange research program.

The House Veterans' Affairs Committee recently asked the VA not to cancel the $9 million study until it can be reviewed by the Office of Technology Assessment and an interagency working group that monitors federal research on the herbicide, which was widely used during the Vietnam War.

A spokesman for Chairman G.V. (Sonny) Montgomery (D-Miss.) said the committee "doesn't understand why the VA suddenly wants to end a study that it has claimed for two years is of some importance."

VA Administrator Harry N. Walters has agreed to delay action until the reviews are complete, an aide said.

The agency already has spent about $2 million on the study, in which VA health researchers are to compare 360 Vietnam veterans with their twin brothers, who served in the military but not in Southeast Asia.

The study was launched after veterans' groups and members of Congress accused the VA of dragging its feet on Agent Orange research. It became the hallmark of this research after the VA was forced to turn over its largest Agent Orange research project, an epidemiological study, to another agency because it had lost its credibility among veterans' groups.

Now the groups and some members of Congress are wondering whether the VA has decided that public pressure for research on the herbicide has decreased.

Dr. Hollis G. Boren, assistant chief medical director for research and development, said he moved to cancel the study in mid-August because it was of "questionable scientific worth."

Boren said an independent scientific panel selected by his office criticized the study's methods and concluded that the number of twins was too small to be "statistically significant." Boren said he also was concerned because the estimated cost of the study had grown more than nine-fold.

But Lt. Col. Alvin L. Young, an Air Force scientist who specializes in Agent Orange research and was an adviser to the VA when it began the twins study, said it would be a mistake to cancel the study.

"This study is extremely important because it gives us an opportunity to measure subtle effects of the war that other studies cannot measure," Young explained. "You have two identical men, which provides a unique way to measure such things as memory loss, sexual dysfunction and sleeplessness."

Young said the study's cost had increased because its scope had increased. Originally it was to focus on possible health problems related to Agent Orange, but it was expanded to examine possible health problems caused by "the entire Vietnam experience."

The controversy has sparked an internal feud among agency scientists. Some contend that Boren's office "sandbagged" the study by appointing what it knew would be a hostile review committee.

"This study has been reviewed by top people and judged impeccable," one VA scientist said. "Twin studies are particularly powerful because most other studies depend upon how accurately you can match one group to a control group. In the case of identical twins, there is no more perfect control."

On the other side, some VA scientists called the study "ill conceived" and a waste of money. "Agent Orange research has become a sacred cow," said one VA official. "Any study that includes those two words becomes politically untouchable, no matter how poorly designed it may be."