UNITED STATES Recent struggles over censorship have focused not on the press, but the arts. There was the attempt, which failed, by a prosecu tor in Cincinnati to prosecute a museum for exhibiting certain photographs the prosecutor called obscene by the late Robert Mapplethorpe, and the attempt in Florida to prosecute on obscenity charges the rap group 2 Live Crew and the conviction of a record-store owner for selling one of their recordings. The press has been able to do its work unvexed. There is still, however, a continuing struggle over the use of the McCarran-Walter Act of 1952 to bar from entry to the United States people whom various administrations have considered to be leftists or undesirable for other reasons. President Bush has Signed into law a bill by Sen. Daniel Patrick Moynihan, Democrat of New York, supported by Sen. Nancy Kassebaum, Republican of Kansas, to forbid the use of the McCarran-Walter Act for such purposes. The relevant portion of the legislation said: "No alien may be denied a visa or excluded from admission into the United States ... because of any past, current or expected beliefs, statements or associations, which, if engaged in by a United States citizen in the United States, would be protected by the Constitution." Senator Moynihan said at the time that ideological exclusions were "dead, done, finished." But Sen. Alan Simpson, Republican of Wyoming, who is very influential on immigration issues, said at the time that despite the legislation, certain foreigners would have to apply for a waiver to the McCarran-Walter Act to enter the United States. "The executive branch has not treated (the Moynihan provision) as repealing the exclusion of communists, but rather as requiring that waivers be granted to permit their temporary entry unless a legitimate reason existed for denying entry," Simpson said at the time. This is, in fact, exactly what has happened. People on the State Department's notorious lists of suspects must ask for waivers. Many of them find that to be a humiliating request, for by asking for waivers they are explicitly admitting that the United States had good reason to keep them out - that they are in fact undesirable leftists or communists or whatever. Bear in mind that the McCarren-Walter Act has been used to keep out or harass such people as writers Gabriel Garcia Marquez and Graham Greene, and such political figures as Hortensia Allende, widow of Salvador Allende, and Yasser Arafat.