NOW THAT the Supreme Court has upheld the administration's regulations reestablishing restrictions on travel to Cuba, the Treasury is moving with a vengence to enforce them. Tourists were first prohibited from visiting Castro's island back in 1963. At the same time, trade and economic sanctions were imposed in an effort to isolate Cuba and to cut off the flow of dollars that might be used to finance communist adventures abroad.

The travel restrictions were removed for a time during the Carter administration, but in 1982 this administration promulgated currency regulations that have the effect of barring travel to Cuba by all except those going to visit close relatives, conduct professional research, engage in official visits or report the news.

The Treasury believes that some travel agencies are trying to get around these restrictions by packaging tours described as "professional research" trips when in fact they are really for sightseers and beachcombers. A Texas travel agency, for example, was penalized for arranging a tour on the pretext that study was intended when the travelers were actually going for the bass fishing, which, of course, would be a dangerous threat to our national security.

The New York Times, in a story this week, reports that a crackdown on tour promoters has now begun in earnest. One Manhattan firm has been forced to turn over travel records of 13,000 clients who have gone to Cuba since 1982. A second subpoena was issued asking for the names of 2,000 lawyers who simply received an advertising brochure about a legal conference in Cuba; the agency has so far refused to comply with this demand.

If you lived through the 1950s all of this may have begun to sound familiar. In those days the government used to deny passports to individuals because of theirpolitical beliefs, a practice struck down by the Supreme Court. Though general travel bans such as the one that applies to Cuba have been sustained by the courts, they are bad policy and can lead to the kind of intrusive list-making we now see.

When the government starts compiling dossiers on who travels where and whether the traveler's reasons for doing so are approved, beware. These Reagan regulations have not specifically been authorized by Congress, and legislators ought to step into the picture to make clear that they intended in earlier statutes to protect the right of Americans to travel.

A strong democracy such as ours has nothing to fear from allowing citizens to see a communist society in operation. And we have a lot to lose by restricting the exercise of this right. Let them all go, grandmothers and journalists, evangelists and political organizers, tourists and fishermen.