Attorney General Edwin Meese III said yesterday that the Justice Department would propose legislation to ban so-called "designer drugs."

Meese said a proposed amendment to the Controlled Substances Act would call for a 15-year prison sentence and $250,000 fine for persons convicted of producing or distributing such drugs.

"The practice of inventing new drugs by changing a few molecules is gaining popularity and leading to the distribution of dangerous new drugs by those intent upon evading the law," Meese said.

Underground chemists produce designer drugs by slightly changing the chemical composition of illegal drugs such as heroin or cocaine. Because existing laws do not prohibit the designer drugs, the drugs have technically been legal.

Although the designer drug may create the same euphoric effect as the similar illegal drug, researchers have found that many have dangerous side effects and some can cause brain damage and even death.

Yesterday, John C. Lawn, head of the federal Drug Enforcement Administration, used emergency powers to temporarily ban two designer drugs that have created symptoms in users that resemble Parkinson's disease, including tremors, slowness of movement and speech and muscle rigidity.

The drugs are MPPP and PEPAP, which are similar to the powerful narcotic meperidine. The DEA has charged that compared to the parent drug, MPPP appears to be five to 30 times more potent and PEPAP 12 to 72 times more potent.