Retired admiral Elmo Zumwalt's testimony before the House government operations subcommittee on human resources and intergovernmental relations {"Ex-Admiral Zumwalt Claims Manipulation on Agent Orange," news story, June 27} was unscientific and unfair, and it manipulated the facts.

In particular, Mr. Zumwalt maligned a member of the previous administration's Agent Orange Working Group and the current director of the Center for Environmental Health and Injury Control at the Department of Health and Human Services' Centers for Disease Control.

Mr. Zumwalt said, "I believe Dr. Vernon Houk has made it his mission to manipulate and prevent the true facts {about Agent Orange use in Vietnam and its health effects on servicemen} from being determined."

Nothing could be further from the truth.

During the past seven years, the CDC has carried out four studies of the health effects of Agent Orange. The results of these studies have been widely reported in the scientific literature -- which means they were rigorously reviewed by many other scientists -- as well as in The Post and other media. We stand behind these studies, none of which established grounds for the kind of charges Mr. Zumwalt has been making.

Be assured that if further studies link Agent Orange to adverse health effects, the public health service will be the first to recognize them -- and propose action.

Until such a time, we are confident in the accuracy and conclusions of the existing studies, and we think it is unconscionable for Mr. Zumwalt to attack the motives of our department and our officials.

JAMES O. MASON Assistant Secretary for Health Department of Health and Human Services Washington