RANSPORTATION SECRETARY Brock Adams again raises a tough question: Hou much are all citizens willing to do-and pay-to provide public transportation facilities that can be used equally well by people in wheelchairs? The secretary's answer amounts to a reasonable attempt to comply with one of those easy-to-order but hard-to-obey federal laws. It is a law that requires that the handicapped not be "excluded from the aprticipation in, be denied the benefits of, or be subjected to discrimination under any program or activity receiving federal financial assistance."

This unqualified order should have been tempered to reflect the limits of what is possible. But that doesn't seem to be in the political offing. So Mr. Adams and others in government have somehow to enforce the rules. To the handicapped, it is matter of rights and of dignity-not of "separate but equal" facilities, which a waiver provision in the new order could permit. But to everyone, it is a question of serious cost. For example, Mr. Adams originally proposed last year that all inaccessible subway stations in New York, Boston, Chicago, Cleveland and Philadephia berefitted-to the tune of some $5 billion to $8billion, according to those cities, and no one knows how much physical disruption for a marginal amount of better service for the handicapped.

So now Mr. Adams is suggesting that all new federally financed facilities be accessible to the handicapped and that the refitting of some existing facilities be undertaken over periods of 5 to 30 years. The price tag for changing existing subway stations, troley terminals, commuter-railroad stations, airports and buses is pegged at $1.4 billion. Also proposed is that, within 10 years, half of all transit buses used during rush hours would have to be accessible have been made for ready addition of wheelchair lifts; in Washington, hundreds of those buses have been purchased and, as a report in yesterday's Weekly sections notes, tests are under way on regular routes.)

But nobody knows how well all these changes will work, how many handicapped people they really accomodate, how much they may cost and how far society is prepared to stretch to make the daily living of disabled people less exceptional. As the argument continues, there will be more questions to resolve, such as how to respond to Mr. Adams' other order that transit authorites pay enormous amount for a "Tranbus" fleet of low-floored vehicles yet to be manufactured. Fro now, it seem the administration is approaching these matters with a more practical sense of what can be done.