One of the oldest provisions in U.S. trade law is set to expire at the end of this month. But don't bank on it. The "manufacturing clause" of the Copyright Act -- on the books in some form or another since 1891 -- has shown a remarkable resistance to efforts to get rid of it, and just may survive this latest deadline, despite a unified attack from interests as diverse as the computer, tobacco and motion-picture industries.

This provision of the U.S. Code simply says that importers may not bring in any overseas printing of a work registered with the U.S. Copyright Office and created by an author who is both a U.S. citizen and resident.

There are a few exceptions: You can bring in a book for your own library, and librarians of academic institutions and others make such purchases for their shelves; books produced in Braille are not covered; imports from Canada are given a loophole; and small quantities of other works -- up to 2,000 copies -- also are allowed in if the Customs Service is told about it. But, basically, a U.S. publisher can't decide it would be cheaper to job out the printing of its latest potential best seller to a shop in Mexico. Printing abroad runs perhaps 15 percent cheaper than similar jobs done in the United States.

The intent back in the 19th century was to give special protection to the U.S. printing industry, then just getting on its feet. It still serves as a protection. Were it eliminated, the International Trade Commission estimates, at least 1,000 jobs in the industry would be lost.

That's enough to make organized labor fight to keep a provision upon which many rely. Labor even has lined up the book publishers on its side of the lobbying battle.

In 1976, Congress decided that the clause should expire in 1982. But when that deadline rolled around, Congress extended it for four more years. President Reagan vetoed the extension as protectionist, but lawmakers overrode the veto. That extension expires June 30, but bills to continue it have strong support in both the House and Senate, despite warnings from Secretary of Commerce Malcolm Baldrige and Trade Representative Clayton Yeutter that they will seek another veto.

Most authors don't like the provision, convinced that they could sometimes strike a better deal for their books with an overseas publisher who would have one press run for the entire English-speaking market. The Authors League of America, calling the manufacturing clause a violation of the First Amendment right to circulate one's views, sued over the issue.

But last month, the U.S. Court of Appeals in New York rejected that argument. Because the clause applies only to works enjoying the protection of the Copyright Act, the judges reasoned that it does not ban the distribution of any ideas. Authors are free to decide against protecting their output and then import as many copies as they wished, the judges noted.

The truth is, though, that the debate over the manufacturing clause has grown so in symbolic importance that it no longer has much to do with authors selling their books or printers keeping their jobs. The provision has become a bogeyman looming over trade issues of much more sweeping impact.

According to some international lawyers, the clause was not in force for a few days before the veto override four years ago -- making it an unlawful barrier to imports under the General Agreement on Tariffs and Trade. That's because the GATT allows old barriers to continue in effect, but only if they stay on the lawbooks continuously.

Europeans view the GATT violation as a green light to impose new trade barriers on U.S. products to make up for the damages they calculate they suffer because of lost sales of printed material. They already have listed U.S. exports of paper products, tobacco, chemicals and printing equipment as the targets of these new controls, set to go into effect if the manufacturing clause is continued past the end of this month. The regulation could cut exports in those areas by more than $500 million.

But the pressure from U.S. businesses to get rid of the manufacturing clause is strongest not from those industries, but from the information-processing industry. The reason: Its efforts to police overseas pirating of software programs are hampered by the fact that the United States never has signed on to the Berne Copyright Convention, the century-old international agreement covering intellectual-property rights. And it is difficult for the United States to join the convention while it has on its books the manufacturing clause, a clear violation of the Berne accords.

In other words, letting the manufacturing clause expire would open the way to adhering to the Berne Convention, which would open the way to getting tougher with software pirates. But those arguments may be a mite theoretical to sell to lawmakers getting calls from printers in their districts who fear that a change in the 95-year-old law will cost them their jobs.

Moskowitz covers legal affairs for McGraw-Hill World News.