CONGRESS MAY BE on the verge of changing the way the nation's commemorative coins are approved and designed.

The proposed change recently came from an unlikely source: the House Subcommittee on Consumer Affairs and Coinage, a subcommittee that in the past has zealously guarded its powers over the nation's coins.

But under the chairmanship of Rep. Richard Lehman (D-Calif.), the panel has espoused a more conciliatory attitude and repeatedly has pressed Treasury officials to be more explicit about what coins they think Congress should issue. By law, the Secretary of the Treasury can on his own decide what coins the nation needs, but in recent years the secretary has yielded that power to Congress.

While that has given the coinage subcommittee a lot of clout on numismatic issues, it also has resulted in a lot of confusion and competing demands for commemorative coins. That has forced the subcommittee to say no to a growing number of proposals.

Lehman's solution, embodied in legislation his subcommittee recently approved by a unanimous voice vote, would shift the burden of determining coin programs back to the executive branch. If approved by Congress, the legislation would require the Treasury Secretary to come up with a five-year plan for commemorative coins.

Members of Congress still would be able to lobby for their favored coins, but the Treasury list would become "something we can stack them up against," said John Ryan of the coinage subcommittee staff.

Only coins that "commemorate any historical event, person, or place of national significance" could be approved by the Treasury and the bill would allow Treasury to issue "not more than one coin program" in any calendar year. Congress could override the secretary's proposed coins, but it would have to give him 18 months notice before it substitutes one of its coin proposals for one of his.

The bill would make a number of other changes, including changing the Mint's official name from "the Bureau of the Mint" to the "United States Mint" and creating a revolving fund to handle the production of all commemorative coins instead of relying on appropriated funds.

It would also meet the demands of a number of artists who dislike the way the Mint selects artists for its coins. Under the bill, coin designs would be reviewed by a seven-member advisory council, one of whom would be the chairman of the Commission of Fine Arts, the federal panel that would continue to have design input. The other council members would be from the arts, museums or numismatic fields.

The Mint, meanwhile, last week made its long-awaited announcement on the numbers of proof coins sets that it is planning to issue in 1990, the first time in recent years that it has ever placed a specific cap on the number of coins it will produce. Equally important was the Mint's announcement that it's trimming the price of Gold Eagle coins, partly to reflect the declining price of gold. Both the mintage limits and the lower prices are expected to boost sales of the gold sets, which have plummeted in recent years.

The four-coin set of Gold Eagle coins will sell for $999 this year, down from last year's price of $1,065, the Mint announced. Eagles containing one ounce of gold, which carry a $50 face value, will sell for $570, down from $585. Half-ounce gold coins, with a $25 face value, will sell for $285, down from $295; quarter-ounce coins, $10 face value, will sell for $150, the same price as last year; and coins with one-tenth an ounce of gold and a $5 face value will sell for $70, up from $65 last year.

Up to 100,000 of the one-tenth ounce gold coins will be offered by the Mint. It will produce up to 63,000 of the quarter-ounce Eagles, 52,000 of the half-ounce and 63,000 of the one-ounce coins. All those levels are below the 1989 sales totals.. Coin shipments should begin in September, according to the Mint.

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