STAMP PRODUCTION in the United States is about to undergo its most profound change in nearly 100 years.

Under an agreement signed last month, private printers will get a bigger share of the Postal Service's $90 million-a-year stamp budget.

The Bureau of Engraving and Printing will remain the nation's primary stamp printer, a job it has had since 1894, but its share of postal business will fall from 90 percent to 70 percent during the next five years.

Moreover, if postal executives have their way, many of the 40 billion stamps needed each year will be printed by firms not currently in the stamp trade, and they'll be making stamps on rolls of adhesive tape, much like Scotch tape.

Equally shocking to some collectors are proposals to print American stamps overseas, one of the many new production ideas being seriously considered at Postal Service headquarters.

This spring, in the midst of negotiations with the Bureau of Engraving, postal officials were advertising for stamp proposals from foreign printers and for multicolored stamps that could be printed on tape using a process called "electronic imaging."

Under terms of the 21-page contract postal officials signed June 11 with the bureau, postal executives have added impetus to seek more outside printers. It calls for private printers to more than double their share of stamps in the fiscal year beginning Oct. 1. Their percentage then should be 20 percent, about twice the current level.

The agreement, which was negotiated after a General Accounting Office report sharply criticized the often acriminous relationship between the agencies, calls for the private share to climb to 25 percent in the next two years and to 30 percent in fiscal 1994 and 1995.

If current tests of self-adhesive and plastic stamps are successful, the private share could be even higher. The agreement covers only "water-activated adhesives" -- stamps that have to be licked -- and excludes other stamp formats.

What collectors will notice under the agreement is that the type of stamps produced by the bureau will change significantly under the agreement. Sheet stamps, until recently the overwhelming majority of bureau stamps, will shrink to 15 percent of the 32 billion the bureau will print next year.

The decline reflects the growing preference for stamps in booklets and rolls, or coils. Booklets will account for 30 percent of the bureau stamps next year, and coil stamps, used by bulk mailers, will amount to 55 percent.

More commemoratives, the stamps for which the bureau has won its most philatelic honors, also are likely to be produced outside the bureau's 14th Street plant.

Warning late last year that the bureau's future as the nation's major stamp printer was uncertain, the GAO recommended that the two agencies resolve their differences in a detailed, formal agreement.

Now that the agreement has been signed, both sides publicly are hailing it as the end to their dispute, saying it will put the relationship on what Postal Service stamp manager Donald M. McDowell calls a more "businesslike" basis. Bureau officials say they are pleased because the contract will allow them to schedule stamp production better and eliminate large amounts of overtime on hurriedly needed stamps.

Terms of the agreement seem to meet bureau demands for longer lead times for major stamps, requiring the Postal Service, for example, to "finalize" its fiscal 1992 plan by March 31, 1991. Art work for stamps using offset and intaglio printing, a popular combination, will have to be presented to the bureau four months before the stamps are to go on sale, a step that should eliminate what the bureau calls "push-ins" to the stamp schedule.

The agreement calls for both agencies to study the feasibility of building a new, single-level stamp printing facility, similar to the bureau's Fort Worth currency plant, an idea strongly supported by postal executives.

CONGRESS HAS given final approval to plans for a set of three commemorative coins next year to help finance repairs to the Mount Rushmore National Memorial in South Dakota.

Under the legislation, sale of the coins could raise as much as $35 million, which would be divided between the Treasury and the Mount Rushmore Memorial Society. The society would use its share for badly needed restoration work on Gutzon Borglum's memorial to presidents Washington, Lincoln, Jefferson and Theodore Roosevelt.

The coin bill, sent to the White House, calls for minting up to 500,000 $5 gold coins, 2.5 million $1 silver coins and an equal number of nickle-copper clad half-dollar coins. Surcharges on the coins would be $35 for the gold, $7 for silver and $1 for the half dollars.

Bill McAllister is a member of The Washington Post national staff.