THE NATION'S coin collectors have found an unlikely advocate in an unlikely spot in the federal bureaucracy.

Diane Wolf, known best as a fund-raiser for Republican causes and art museums in New York and, at age 33, the youngest presidential appointee to the federal Commission of Fine Arts, is pushing a redesign of the nation's coins.

Our pennies, nickels, dimes and quarters are poorly designed, out-of-date and dull, Wolf argues. A novice collector herself, she says coins are the "art that people touch every day" and that Americans deserve better-looking ones.

The commission, a seven- member panel that reviews the designs of proposed buildings and monuments in the nation's capital, has become Wolf's pulpit.

As the commission's lay member, Wolf has seized on the agency's power to review "medals, insignia and coins" (granted in 1921 by Warren G. Harding) and won unanimous support for a resolution urging the Treasury Department to consider new coin designs.

"This is an all-round winning proposition," Wolf says, because changing the designs should boost the sales of coins to collectors, pumping $2 billion into the Treasury in the first year.

And as any Reagan appointee knows, coming up with ways to cut the deficit should win Wolf plaudits.

Thus far, however, Wolf's biggest backers are numismatists; her coin call has been the talk of the trade press. Of a thousand letters she's received, she says, only four have been negative.

The reaction at Treasury and on Capitol Hill has been less enthusiatic. A spokesman for the Bureau of the Mint says Treasury officials have talked to Wolf and have "an open mind" on the subject. But, the official says, there are no plans to change our coins, some of whose designs are controlled by law.

Curtis Prins, staff director of the House subcommittee on consumer affairs and coinage, is pessimistic. "I don't see any great push for it," he says. "From what I can tell, this is a one-woman crusade."

The Treasury historically has opposed such efforts, Prins says, and many on Capitol Hill, including coinage subcommittee chairman Rep. Frank Annunzio (D-Ill.), think there are more urgent problems with the nation's coins.

Examples, he says, are the Susan B. Anthony dollar, a marketing disaster despite extensive research that said it would be a much-needed coin; and the John F. Kennedy half-dollar, which virtually has disappeared from circulation.

What seems undisputed is that the Mint is certain to be issuing more commemorative coins. Wolf takes credit for pressuring the Treasury into holding a design competition for the $5 gold and $1 silver coins that will be placed on sale this summer to mark the 200th anniversary of the Constitution.

Treasury Secretary James A. Baker III will be in Philadelphia July 1 for the striking of the first of those coins, illustrating his support for the project. And Prins notes that 1988 should see commemorative coins for the Olympic games and that 1989 will see coins for the 200th anniversary of Congress.

"It's not that we haven't paid attention to the request for more coins," Prins says.

Although the law allows the Treasury secretary to change some coins after they've been in circulation for 25 years, he's not permitted to change some of them very much. For instance, the quarter must have an eagle on one side and George Washington on the other, unless Congress changes its mind.

Wolf is undaunted. "The one thing I'm learning about Washington is you have to follow up on your ideas," she says.

"The Mint, pun intended, should be a money-making proposition."

Bill McAllister is a member of The Post's national staff.