American know-how does it again, folks.

An Ohio doctor has combined Teflon, that miracle of the frying pan, with guns, those miracles of the American Bill of Rights, to give us Teflon bullets which, at 357 magnum, will punch through four bulletproof vests and then have enough juice to punch through 2 1/2 phone books. It's not the phone company that's worried, it's police departments and anybody who needs to wear a bulletproof vest, says "NBC Magazine," tonight at 8 on Channel 4.

The segment opens with -- what else -- footage of President Reagan being shot last spring. Then firing tests demonstrate that the Teflon KTW bullet might be able to pass through a Secret Service agent and still have enough power to go on and kill whoever was being protected.

The segment doesn't mention that such a bullet would leave a far cleaner and narrower wound than the standard mushrooming variety now available. But a clean wound isn't much comfort when it's right through, say, your head.

Dr. Paul Kopsch, a former coroner, sits in front of shelves covered with pistols and defends his KTW bullet. "The best way to make the good guys healthy is to make the bad guys sick. Real sick."

The show doesn't explore just what use the bullet would be against criminals, who, after all, don't usually wear bulletproof vests. It would have been good ground for either attacking or defending the KTW bullet, but it gets short shrift, in favor of pleas for laws banning the KTW from police officials and Rep. Mario Biaggi (D-N.Y.), who was wounded 10 times during his New York police career.

The zillion-dollar Florida drug smuggling industry should prove a major consumer. One police official points out that the bullet is said to be good for puncturing the hulls of Coast Guard ships.

It is said to be available at gun stores.

Says Kopsch, on the ethics of it all: "If a thing is technologically possible it will be invented. If it is invented it will fall into evil hands. I can't take credit every time it falls into evil hands."