LOS ANGELES (AP) _ A half-inch-long, stainless steel tube that may have saved Mother Teresa's life is at the center of a dispute over the Food and Drug Administration's pace in approving experimental medical devices.

In December, the lining of Mother Teresa's major coronary artery tore as doctors unclogged it with a tiny balloon. So they implanted a tube known as a Palmaz-Schatz stent to seal the tear, hold the artery open and prevent a heart attack. The 81-year-old nun left the hospital last month.

Mother Teresa's doctor and several other researchers conducting a nationwide study of the stent contend red tape and sluggishness at the FDA prevent thousands of American heart patients from getting the lifesaving tube.

Other doctors say the FDA is exercising proper caution by sharply limiting use of the stent before deciding if it is safe and effective for widespread use. They say the stent can have dangerous side effects, including the heart attacks it is designed to prevent.

The agency isn't expected to approve the stent until mid-1993, three years after an application for approval was submitted by the manufacturer, a Johnson & Johnson subsidiary. That's twice the FDA's average 1 1/2 -year approval time.

The Palmaz-Schatz stent has been studied longer than three other models. It already is used in many countries.

''This device helped Mother Teresa, but many other patients who could benefit are unable to receive it due to a bureaucratic problem at the FDA,'' said Dr. Paul Teirstein, a cardiologist at the Scripps Clinic and Research Foundation in La Jolla who treated the Nobel Peace Prize winner. ''I'm very frustrated. I can't deliver adequate care to patients.''

But Dr. Sheldon Goldberg, cardiology chief at Thomas Jefferson University Hospital in Philadelphia, countered: ''This is a permanent implant. It should come under the most careful scrutiny.''

FDA spokeswoman Susan Cruzan said the FDA ''tries to obtain all the answers to safety and effectiveness issues'' and will decide whether to approve the stent ''only when we have received this information to our satisfaction.''

Palmaz-Schatz stents have been implanted in 1,350 Americans in a study that started in 1988. The FDA halted most implants in November because it considers 1,350 patients sufficient for the agency to decide if the stent is safe and effective.

Until the FDA makes that decision, doctors can implant stents only in emergency patients such as Mother Teresa who are at risk of imminent death, or in patients who had bypass surgery but whose replacement vessels became clogged.

Many non-emergency patients who now can't get stents will get sicker and endure repeated, often unsuccessful balloon angioplasties or emergency bypass surgery, said Dr. Craig Walker of Louisiana's Cardiovascular Institute of the South. A balloon angioplasty is the artery-unclogging procedure Mother Teresa underwent.

Dr. Martin Leon of Washington Medical Center, Johnson & Johnson's paid consultant for the stent study, estimated 50,000 Americans annually could benefit from stents.

Leon and others said the FDA is slow and overly cautious, especially because devices such as silicone gel breast implants and implanted mechanical heart valves developed problems after the agency allowed their widespread use.

Stents ''are being withheld for reasons that are as much political and administrative as scientific,'' Leon said.

Dr. Richard Schatz, a Scripps Clinic researcher and stent co-inventor, said the FDA needs a way to allow continued use of a promising device pending final approval. ''The perception of every guy in the (research) group is that these things work,'' he said.

But Dr. Eric Topol, cardiology chairman at Ohio's Cleveland Clinic, said, ''I don't believe there's any good reason to become FDA-bashers.'' He said blood clots develop in 5 percent of stents, requiring repeat angioplasties and sometimes causing heart attacks.