Some 209,000 enlisted personnel in the Army use marijuana and nearly 49,000 use hard drugs such as heroin and LSD, figures in an internal Army survey indicate.

However , Brig. Gen. John H. Johns told the House Select Committee on Narcotics Abuse and Control yesterday that the Army was unable to determine whether the use of drugs had any measurable effect on combat readiness.

Johns, director of human resources development in the Army's personnel office, said the survey indicated drug abuse in the military is not as wide-spread as shown by an earlier committee study.

"The Army views its drug abuse problems as serious but not of epidemic proportions," Johns said.

"The abuse does have some degree of adverse impact on combat readiness but it is difficult, if not impossible, to established a definitive casual relationship that can be quantified," he added.

In April, Rep. Lester Wolff (D.N.Y.), the panel's chairman, took a different stance. Commenting on his committee's survey, Wolff said, "the committee is certain that regular drug use does have an adverse effect on combat readiness, job performance and the morale of our armed forces."

Johns was testifying on the Army's random survey of enlisted soldiers, in which they were asked whether they used drugs occasionally, frequently - roughly 31 percent of the 671,000 enlisted men and women, slightly more than 209,000 would have admitted using hard drugs.

The survey was attacked by Rep. Glenn English (D-Okla.:), who noted that 50 percent of those responding said they believed the answers could be traced to them.

"It is a crime in the Army to use hard drugs and marijuana, English said, questioning whether many soldiers might have answered untruthfully in order to avoid being linked to a crime.

"Even with the threat of prosecution, even under the threat that the survey could be traced back to them, 30 percent answered yes" to marijuana use, he noted.

English also criticized the questions, saying they allowed the person answering to determine whether his or her use was an occasional or frequent.

"A person who smoked 5 marijuana cigarettes a day could decide he was an occasional user," he noted.

Johns said the Army data indicated there had been a decrease in hard drug abuse and that marijuana usage was holding steady.

He acknowledged that the overall use of drugs in the Army was higher than estimates on drug abuse among civilians. But Johns pointed out that drug abuse in society is at its highest in the 18-to-25 age bracket and that, within this age group, the majority of abusers are male.

"The Army has a higher concentration of persons in the 18 to 25 bracket than society in general and they are predominantly male," he said.