COUNT AMONG the stranger steps taken recently in the name of national security the May decision by Boston Customs Service officials to block delivery in the United States of about 30,000 Cuban publications by invoking a musty provision of the 1917 Trading With the Enemy Act. Although banned in Boston, the Cuban newspapers and magazines -- primarily copies of the official Communist Party paper Gramna and similarly tedious tracts -- presumably continue to reach their readers unhindered through other ports of entry, at least for the moment. Subscribers to the Cuban periodicals have protested the unexpected decision to enforce the seldom-used World War I statute, one in which -- according to a department spokesman -- officials at State "played no role."

Those who wish to contine receiving the publications, as matters stand, can either purchase them from three licensed New York-based distributors or apply for a license as an "importer" from Treasury's Office of Foreign Assets Control. Treasury spokesmen argue -- unpersuasively -- that the Boston seizure neither reflects a new policy nor indicates any desire to find out "who reads what" but was aimed primarily at "trying to get a handle on any money which goes to Cuba." But Treasury's defense of its licensing scheme makes sense mainly to students of Catch-22 government logic: those Americans not involved in reporting or research can obtain licenses for the Cuban materials only if they receive the material free of charge , not if they pay for it (a "privilege" reserved for professional users under the law). Customs intends not to "get a handle" on exported money, in short, but on domestic readers of the publications.

Exactly 60 years ago, Supreme Court Justice Oliver Wendell Holmes wrote that "the use of the mails is almost as much a part of free speech as the right to use our tongues." In this connection, the government record of dealing with reading material deemed "subversive" has been a dismal one for much of the century. During World War I, as a result of the Trading With the Enemy Act and other statutes, not only could actual German propaganda be seized but the postmaster general even gained virtually unlimited censorship powers over the American foreign-language press.Enemy writings entering the country were seized as a matter of course during the World War II, and, prior to 1958, when it bagged "Communist propaganda," the Post Office did not bother even notifying Americans for whom the material was intended. Then, for several years until the Kennedy administration halted the practice, the Post Office sent people notices that such mail awaited them if they would sign forms indicating that they wanted delivery.

As late as 1965, the Supreme Court unanimously struck down -- as a direct violation of the First Amendment -- another dangerously silly effort to regulate incoming mail, the 1962 Cunningham Amendment, which banned foreign "Communist political propaganda" from the U.S. mails. Later, during the Vietnam War, the government made sporadic efforts to withhold Chinese and North Vietnamese tracts when they arrived in this country.

That unhappy legacy seemed behind us until this latest seizure. Why now? Did the sudden increase of Cuban printed material in Boston provoke local customs officials to take unwise steps on their own initiative? Or if, as the State Department insists, "no change of U.S. policy was involved," what more can we expect in the way of government restraints on imported reading matter? As for "trading with the enemy," why move against Cuba alone and not the Soviet Union and other declared adversaries? Better yet, so far as printed materials are concerned, why not let sleeping statutes lie?

Whatever the technicalities of a vestigal measure like the Trading With the Enemy Act, the petty harassment displayed by Treasury bureaucrats should be stopped before it spreads. The Customs Service is overburdened enough with serious tasks to allow the diversion of its agents to such unnecessary mischief. Even in Boston, Americans need no license nor any special government permission to exercise their First Amendment rights to read -- if they wish to -- even the most feckless examples of a tyrant's flackery.