THEY WERE QUITE a couple, wandering the halls of Congress last year. There was the tiny Elvira Clain-Stefanelli, executive director of the National Numismatic Collection, and a big, beefy Smithsonian Institution guard, lugging a briefcase filled with some of the nation's rarest coins.

But, as Smithsonian Secretary I. Michael Heyman noted earlier this month, Clain-Stefanelli's passionate pursuit of congressional support for commemorative coins to mark the institution's 150th birthday promises to pay off handsomely. If all 100,000 gold and 650,000 silver coins are sold, the Smithsonian will get $10 million from surcharges on the coins. Of that $1.5 million will be earmarked for its coin collection.

That was reason enough for Clain-Stefanelli and other coin advocates last year to urge Congress to lift its moratorium on new commemorative coins and endorse the Smithsonian coins. It did by an overwhelming margin, Heyman pointed out.

Mint Director Philip N. Diehl told a crowd of dignitaries gathered at the National Museum of American History for the Aug. 7 presentation of the first coins to Heyman that he believed the commemoratives would be a sellout. He predicted that the 1.5 million collectors listed on the Mint's mailing lists "will rush to buy these coins."

Given Diehl's public condemnation of recent coin programs and a critical General Accounting Office report released that day, his remarks had special significance.

Heyman told the gathering that it was highly appropriate that the federal institution celebrate its 150th anniversary with coins because "but for coins we wouldn't be here." He was referring to the 104,960 British gold sovereigns that arrived in the U.S. in 1838 from the estate of James Smithson, a Briton who left his fortune for creation of "an establishment for the increase and diffusion of knowledge" in America, a country he had never visited.

Congress had stipulated that the $5 Smithsonian coins could be minted in platinum, but the Mint decided that gold would be more appropriate since Smithson's gold coins had provided the financial foundation on which the Smithsonian Institution was built. The coins carry Smithson's profile on the obverse and the institution's sunburst logo on the reverse.

The silver dollars carry the first Smithsonian building on the Mall, the Castle, and on the reverse feature an allegorical figure sitting atop the world and carrying the torch of knowledge. Both coins carry the phrase "for the increase and diffusion of knowledge" from Smithson's will.

Until Sept. 13, the coins will be sold at "pre-issue" discounted prices. The silver coins will sell for $33 each in polish proof condition and $30 in uncirculated condition. The gold coins will sell for $195 in proof condition and $180 in uncirculated condition. Sets with both coins in proof condition will sell for $217. THE SAME DAY that the Smithsonian coins went on sale, Congress received additional warnings about the troubled status of commemorative coin programs. A General Accounting Office report, released by Sen. Alfonse M. D'Amato (R-N.Y.), chairman of the Senate Banking Committee, indicated that the problems may be more serious than Mint officials had suggested.

The report added several recent coin programs to those that have previously been reported as money losers. The GAO said the Mint lost $4.9 million on programs that ended in 1994 and 1995. In addition to the previously reported loss of $4.1 million on the 1994 World Cup coins, it said the Mint lost $100,000 on the 1989 U.S. Capitol commemoratives.

As of March 31, the GAO said the Mint also had losses of $400,000 on the 1995 Civil War commemoratives and $300,000 on the 1995 Special Olympics silver dollar. The latter figure was calculated before a final sale of the remaining 263,551 of the coins.

The Mint reported another $3.2 million loss on the large Olympic coin program for the Atlanta Games as of March 31, but the GAO said it attributed this loss to "high start-up costs" and expected to make up the loss with sales during the Games.

In a July 15 letter to Congress, the Mint disclosed that it has revised its accounting procedures for the Olympic coin program and it had registered a $1 million loss through June 30. "The Olympic coin retail program continues to perform well below expectations," the report said. "While the Games and the immediate post-Games period is expected to provide a boost to retail sales, it is unlikely to make the retail program profitable."

Separate numismatic and international sales of the coins are expected to remain "firm into fiscal 1997 and to offset losses associated with the retail program, allowing the entire Olympic program to break even or post a small profit," the Mint said.

A solution may be to place commemorative designs on circulating coins, something that the leaders of the House Banking Committee have started to promote, the GAO noted. Legislation, introduced by Rep. Michael N. Castle (R-Del.), calling for placing a design for each of the 50 states on the nation's quarters has cleared the House banking subcommittee responsible for coinage issues and is expected by Castle's staff to reach the House floor in September. FOR INFORMATION on the Smithsonian coins, contact Customer Service Center, U.S. Mint, 10003 Derekwood Lane, Lanham, MD 20706-2255. Phone: 800/283-2646. Next week in this space: Photography columnist Frank Van Riper reflects on how times have changed during his professional career. CAPTION: The Mint predicts a sellout for the Smithsonian commemorative silver dollar.