A federal program that has provided free marijuana to the seriously ill is being phased out by Health and Human Services officials who have concluded it undercuts official Bush administration policy against the use of illegal drugs, according to HHS officials.

While a small number of patients already receiving marijuana will continue to do so, new applicants will be encouraged to try synthetic forms of delta-9-THC, the psychoactive ingredient in marijuana, rather than the weed itself, according to a new policy directive due to be signed by James O. Mason, chief of the Public Health Service.

Mason said yesterday he was concerned about a surge in new applications in recent months, especially from AIDS patients, and the message it would send if HHS were to approve them.

"If it's perceived that the Public Health Service is going around giving marijuana to folks, there would be a perception that this stuff can't be so bad," said Mason. "It gives a bad signal. I don't mind doing that if there's no other way of helping these people. . . . But there's not a shred of evidence that smoking marijuana assists a person with AIDS."

But his decision drew angry criticism from pro-marijuana activists who contended that many AIDS and cancer patients have found the drug invaluable in combating the nausea caused by their treatments.

"This is ludicrous," said Kevin Zeese, vice president of the Drug Policy Foundation, a group that has promoted the use of marijuana for medical purposes. "What they are going to do is deny medicine to very sick Americans for political reasons. . . . This shows the cruelty of the war on drugs."

Zeese noted that Herbert D. Kleber, deputy national drug control policy director, had touted the program on national television as a "compassionate" option that was available to seriously ill patients.

But while the new HHS policy has been in the works for more than two months, officials said this week they did not believe the drug control policy office had been consulted. Kleber was out of town yesterday and could not be reached for comment.

The new policy is the latest development in a debate about marijuana's classification under the drug laws. The Drug Enforcement Administration has denied that marijuana has any therapeutic value and has classified it as a Schedule I drug, the same as heroin, forbidding doctors to prescribe it.

But last April, the U.S. Court of Appeals for the D.C. Circuit ordered the DEA to reconsider its stand after concluding that the agency had acted unreasonably in evaluating the drug's possible effectiveness.

In addition, a recent survey by Harvard University researchers found that nearly half of 1,035 cancer specialists who responded reported that they would prescribe marijuana to their patients if it were legal to do so.

For the past 15 years, pre-rolled cigarettes of marijuana -- grown at a National Institute on Drug Abuse (NIDA) research farm in Oxford, Miss. -- have been provided to a handful of such patients. But officials said applications began to increase markedly following publicity over the case of Kenneth and Barbra Jenks, a Florida couple suffering from AIDS.

Convicted of violating the state's drug laws last year, the Jenkses applied and won Food and Drug Administration approval to use the drug as an "investigative new drug." While only six people had received marijuana under the program before last summer, the FDA has received 28 applications in the past year, and was concerned that it would be swamped with hundreds more in coming months, officials said.

Pro-marijuana activists "were beginning to promote this . . . it was becoming a kind of 'write in and here's how you do it' kind of thing," said Jeffrey A. Nesbit, an FDA spokesman.