There are miracles, and then there are miracles. Modern Medical Breakthroughs (9 p.m., Ch. 2) will show both.

First, the NBC documentary special will introduce you to the miracles of modern medical technology with a number of real-life vignettes that show how scientific advances have improved the lives of unfortunate victims of circumstance. At the same time, however, "Modern Medical Breakthroughs" pays tribute to the courage of those victims whose indefatigable spirit seems pretty miraculous in and of itself.Take Bill Demby. As a young man he dreamed of one day playing in the National Basketball Association, and the athletic skills he demonstrated during his youth gave him good reason for maintaining hope. But a tour of duty in Vietnam ended those dreams with one explosion of enemy fire, during which he lost both of his legs.

That would have been the end of the story for many men, but not for Bill Demby. His search for a better way of life led him to Seattle, where Boeing engineers developed a prosthetic foot so lifelike that Demby today has no trouble going one-on-one with the high schoolers he talks to about making the best of the hand that life deals you.

"You do the things you can," he tells a class of students, which poignantly includes a young girl in a wheel chair. "The things you can't do . . . well, you just work a little harder."

"All the technology in the world can't compensate for the human spirit," adds narrator Gregory Harrison. "It's courage that puts you back on top."

That same kind of courage is seen in a segment featuring David Butterfield, a sports filmmaker who was suddenly rendered deaf for reasons doctors still don't fully understand. Thanks to a new device called the Cochlear Implant, Butterfield has overcome his handicap and resumed his life and career. And then there's Dr. Francisco Bucio, who lost four fingers when a building collapsed on him during the tragic Mexico City earthquake, but who now is able to perform microsurgery because two of his toes have been transplanted to his hand.

Also covered during the special is a new surgical procedure that can cure violent epileptic seizures and innovative techniques that are being used to teach deaf children to communicate in exact English.

In all cases, one can't help but be touched by the skill of the scientists and the tenacity of the patients profiled in "Modern Medical Breakthroughs." They are dreamers all. And as Harrison concludes, "Today's dreams are tomorrow's breakthroughs."

* TONIGHT'S YOUR CHANCE to decide whether or not a program will continue on NBC.

No, we're not talking about "A Year in the Life" or "Aaron's Way." Would that it were so. We're talking about Home Free, a new hour-long series that premieres tonight on Ch. 2 at 7 p.m.

The show stars Michael Warren ("Hill Street Blues") as a foster father who cares for six troubled teenage boys. The series will focus on how Warren and stay-at-home caretaker Eddie (played by Trinidad Silva) help the young men grow and face the harshness in their lives by giving them love, guidance and acceptance.

At least, that's what the series will be about if NBC picks it up. So far it isn't in the network's future plans, which is why MTM, the show's production company, has launched a full-scale media assault to tell audiences about the show and invite them to watch it.

"NBC has told us that a 25 (ratings share) will make us a definite mid-season pickup, and we need a 22 to even talk about it," said producer David Milch.

So they have placed ads in publications nationwide, inviting viewers to "program the #1 network."

"If you want great TV, get involved," the ads proclaim. "WATCH IT! You'll laugh, you'll feel good and you'll want to live there. We guarantee it!"

Those are strong words. But remember, this is the same company that brought you "St. Elsewhere," "Hill Street Blues" and "The Mary Tyler Moore Show," so they know what it takes to back up such strong promises.

I haven't see it yet, but the MTM bloodlines make "Home Free" sound like a pretty good risk to me. Give it a try. If nothing else, you'll have the satisfaction of telling those NBC hotshots what to do.

* GREAT NEWS, comedy fans. CBS has announced that is going to bring back The Smothers Brothers Comedy Hour after all. Tom and Dick will return with six new episodes of their wonderfully eclectic variety show in late September, due largely to the fact that their company has an independent agreement with the Writers' Guild that allows their writers to work during the strike.

See? Every cloud does have a silver lining.

* WHICH REMINDS ME, if you were thinking of using the strike as the perfect springboard to your screenwriting career, think again. The Writers Guild took out a newspaper ad last week promising that scab writers will never work in Hollywood after the strike is solved. "Your future is at stake" the ad threatened.

Of course, they are assuming that the strike will indeed be solved eventually, and to tell you the truth, I'm not so sure about that. Still, consider yourself warned. We'll be inspecting your typewriter for tell-tale signs of creativity next week.