Tom McMillen has been playing basketball long enough to know that a smart player keeps his opponent wondering what he is going to do for as long as possible. Now, as his pro basketball career winds down, McMillen is beginning to apply that basic principle to his next chosen vocation--politics.

But politics is not a game where one can tinker and experiment the way one can over the course of an 82-game basketball season. Opportunities come only every two years. What's more, politics is so full of gossip and schemes, keeping a secret is about as easy as being 6 feet 11 and walking into a room unnoticed.

And McMillen has made it clear he does not want to go unnoticed. Nine years ago, he graduated from the University of Maryland and went on to Oxford as a Rhodes scholar.

But from there he launched what has been a very ordinary career in pro basketball, bouncing through several NBA cities before landing with the Washington Bullets two weeks ago.

The Bullets play their home games in Maryland, and McMillen long ago established residency in Crofton, about 20 minutes from the Capital Centre and right in the heart of Rep. Marjorie Holt's congressional district. Holt is the only Republican in the eight-member Maryland congressional delegation, and McMillen would love to challenge her for that seat next year.

The trade of McMillen from the Atlanta Hawks to the Bullets was obviously a favor to him from Hawks owner Ted Turner, who likes McMillen enough to have thrown a fundraiser for him, and Bullets owner Abe Pollin, a long time friend of Peter F. O'Malley, the Democratic power broker of Prince George's County.

McMillen now can have at least one more season of basketball at his current salary of $200,000, before he decides whether to challenge Holt. In the meantime, by playing coy and saying he is "considering" a run at the seat, McMillen can keep his opponent--and the media--at least a little off balance.

If he announced his candidacy now, there could be all sorts of technical problems this coming season. Could Holt demand equal time if McMillen appeared on television as a half-time guest?

What's more, once a candidate ends the suspense by announcing he is running for office, the media tends to lose interest in him for a while.

By not announcing, McMillen also makes it somewhat more difficult for Holt to attack him. She already has sent out a fund-raising missive mentioning him as an opponent, but until McMillen formally gets into the race, she will have to pull her punches.

Thus, as basketball season unfolds, McMillen can continue to test the waters. He has certainly done his homework the last few years. In addition to raising considerable funds nationally for the Democratic Party, he has been as omnipresent as any politician in Maryland, seemingly appearing any time two Democrats are together.

Some more experienced politicians think McMillen should start at a lower level by running for the state legislature. But McMillen, who fancies himself something of a poor man's Bill Bradley, clearly believes he can trade on his name, his physical stature and the background work he has done to challenge Holt.

If Holt appears unbeatable or if the economic indicators are so encouraging that it begins to look like a bad year for Democrats, he can always say that he's only 31 and that he'd like to play basketball for another year or two. At his salary no one would blame him.

For now, however, McMillen will continue to be the smart ballplayer he always has been. He will stand calmly on one corner of the court, use his peripheral vision to see what is unfolding around him and then make his next move.

Abe Pollin has been kind enough to give McMillen the ball and the home court advantage with his trade. It's a pretty good bet that McMillen will be driving right at Holt by this time next year.