The Drug Enforcement Administration announced yesterday that it would outlaw the hallucinogen MDMA, known informally as "Ecstasy," because research on a similar drug showed that a single dose may cause permanent brain damage.

DEA Administrator John C. Lawn said he had signed an emergency order placing the drug in the Schedule I category of drugs with the most serious potential for abuse. These include heroin and cocaine.

MDMA has been used by therapists and psychiatrists as an aid in psychotherapy. Now, it will become illegal July 1.

"All of the evidence DEA has received shows that MDMA abuse has become a nationwide problem and that it poses a serious health threat," Lawn said. ". . . This emergency action is a stopgap measure to curb MDMA abuse until the administrative process can be completed."

A recent University of Chicago study has shown that a drug very similar to MDMA causes brain damage in laboratory animals, sometimes after a single dose. Researchers told the DEA that MDMA could be expected to cause the same damage in humans.

Gene R. Haislip, head of the DEA's Office of Diversion Control, said the drug was available in at least 21 states and Canada and is especially popular with college students and young professionals.

Areas of concentrated use include California, Texas, Florida, New York and New England, he said.

Haislip said he could not estimate how many people use MDMA. DEA agents have said they believe that 30,000 tablets are being distributed each month in one Texas city.

Proponents of MDMA, technically 3,4-methylenedioxymethamphet-1.824 PTS LEFT amine, say it can make people trust one another and break down barriers between lovers, parents and children, therapists and patients.

Under Schedule I, production or sale of MDMA would be punishable by as much as 15 years in prison and a fine up to $125,000. Lawn took action under emergency authority granted him by the Comprehensive Crime Control Act of 1984, which allows the DEA to ban a substance for a year.

Meanwhile, the agency is working with the Food and Drug Administration on an MDMA study expected to last nine to 18 months and perhaps result in permanent restriction. Public hearings are planned.

The FDA has never approved MDMA and has no jurisdiction over it as long as the drug is not involved in interstate commerce. It has been left to the states to regulate.

Although the formula for the drug has been patented since 1914, according to the DEA, it is being produced only by clandestine laboratories.

Haislip said the price of an MDMA tablet ranges from $8 to $20. Sales have been promoted through distributions of such pamphlets as, "Ecstasy, Everything Looks Wonderful When You're Young and on Drugs" and "Flight Instructions for a Friend Using XTC." Other street names for the substance are XTC, Adam, and Essence.

Haislip said use of MDMA was known to have resulted in two deaths, including that of a California psychoanalyst with a heart condition who died 30 to 60 minutes after taking a 200-milligram dose. The usual dose is between 50 and 110 milligrams, officials said.

Haislip said drug-treatment authorities in California were beginning to report seeing individuals who had taken multiple doses of MDMA, with symptoms of "severe anxiety reactions, paranoia, fear, sleep problems and depression."

MDMA, a "designer" drug, is a slightly altered copy of now illegal MDA.