Thalidomide, once the world's most notorious drug, won Food and Drug Administration approval Thursday to be sold in this country - but with unprecedented restrictions aimed at avoiding the birth-defect horrors of the 1960s.

The FDA said thalidomide effectively treats a small number of leprosy patients - no more than 50 Americans a year - who suffer an agonizing inflammation.But thalidomide becomes the most restricted drug ever sold in the United States. Every American, male or female, who uses the drug will be required to enroll in a government-monitored registry. And its maker, New Jersey-based Celgene, will allow prescriptions to be dispensed only by precertified doctors and pharmacists. Women must undergo pregnancy tests before getting the drug, and men and women must use contraception.

Nevertheless, doctors are free to prescribe drugs for any disease they see fit, and thalidomide is being tested as a possible treatment for AIDS-related ulcers and wasting, lupus, even cancer. So the FDA acknowledges that thalidomide ultimately may be prescribed for many more people - and critics warn that one day another thalidomide baby probably will be born.

Thalidomide was banned worldwide 35 years ago after it caused horrific birth defects in 12,000 babies. It had been sold as a sedative for pregnant women in 48 countries - but never in the United States. The FDA made its name as the nation's medical watchdog after an agency scientist uncovered early signs of toxicity and blocked thalidomide's approval here. Still, some Americans got it overseas or in clinical trials.