THE WAITING ROOM of the train station in Hoboken was an appropriate place for the announcement by Vice President Mondale that the Carter administration has discovered mass transit. The station is somewhat off the main track, just as the administration has been on this subject, and it represents an industry that is, also like the administration, in need of revitalization.

The $13-billion program the vice president outlined would certainly do wonders for mass transit. There is money in it to double the production of commuter buses (useful in small as well as large cities), expand modernization programs on existing rapid transit lines, and speed up construction on new rail lines that have already been approved.

These are programs the Department of Transportation has been trying to foster for years. But until the vice president spoke, the Whate House had not been noted for its support of them. Just a month ago, for example, the White House tried to kill an arrangement that had been worked out to permit completion of this area's transit system -- Metro. It may be that the beating the White House's lobbyists took that day on Capitol Hill caused a rethinking of the administration's mass-transit policy.

Unfortunately, the new policy has a string attached to it. "Without the windfall-profits tax, all this is just rhetoric," Vice President Mondale said. If he means that, the administration has yet to discover the values and needs of mass transit. All it has discovered is the political appeal of transit programs in urban areas.

In that context, the $13-billion figure is being dangled out there to persuade members of Congress from urban areas to vote for the excess-profits tax. The money may be a strong enticement -- the transit program would reach a high percentage of the nation's population in cities as different as New York and Peoria -- and the ploy may turn out to be a good one, politically speaking.

But the link the administration is trying to forge between mass transit and the excess-profits tax is a bad one. The needs of mass transit will exist whether or not the tax is passed. If the administration is prepared to support a major mass-transit program only if an excess-profits tax is passed, it has yet to get its priorities straight.

Any energy conservation program worthy of its name must contain substantial incentives for the expansion of mass transit. The administration would have been wiser to support a program aimed at achieving that expansion and point to the excess-profits tax as one to fund it. As it is, the administration is risking the loss of a program the country needs by tying it to a specific tax that may, or may not, be approved by Congress.