Maryland Rep. Tom McMillen and Anne Arundel County lawyer Jack A. Blum agree on at least one hard fact about American politics: Money talks.

But Blum, who is challenging McMillen in Tuesday's 4th District Democratic primary, is gambling that he can make political poverty talk even louder.

A former congressional investigator, Blum has cast his campaign against McMillen as a referendum on modern political fund-raising practices, pointing out that McMillen, like many incumbents, has collected thousands of dollars from interest groups he regulates on Capitol Hill. To dramatize his opposition to this campaign finance system, Blum has refused to raise money at all.

The result is a race that, in financial terms, could hardly be more lopsided: Blum has spent $500 of his own money, while McMillen has raised more than $400,000. Senior Democratic politicians in Maryland's 4th District say McMillen's chances of defeating Blum are almost as good as his financial position.

But Blum says that being a long shot has given him the freedom to run the kind of campaign he believes voters want.

"This way, I can say things and do things without worrying about whether I offend contributors," said Blum. For Blum, that freedom has meant he talks about little besides campaign financing.

McMillen, a longtime acquaintance of Blum's, is not concerned enough about Blum's challenge to spend much of the money he has raised; his campaign has not purchased any broadcast advertisements and instead is emphasizing person-to-person campaigning. And McMillen says that Blum, in his general criticisms of political fund-raising, has a point.

"Jack is running against the system," McMillen said. "But what he is saying you could say in every congressional district in the country.

"I agree we should reform the {campaign finance} process and we should have a much tougher law. I voted for one . . . . But I think there's a certain cynicism to Jack's position that members of Congress can be bought and sold. I think I have represented the district well on a variety of issues and the voters will show confidence in me."

McMillen is seeking a third term representing the 4th District, which includes Anne Arundel County, southern Prince George's County and southeastern Howard County. Along with McMillen and Blum, the Democratic field includes John W. Dotterweich, a supporter of political extremist Lyndon H. LaRouche Jr.

The district's Republicans have a three-way primary Tuesday that features two former federal administrators and first-time candidates, Robert P. Duckworth, of Crofton, and Michael D. Hathaway, of Accokeek, and the man McMillen defeated overwhelmingly in 1988, upholsterer Brad McClanahan. McClanahan is awaiting trial on a drunken driving charge.

The winners of the two primaries will meet in November. Registered Democrats outnumber Republicans in the 4th District by a ratio of almost 2 to 1.

McMillen, 38, made himself a familiar name as a young man, when he was a basketball star at the University of Maryland. By the time he returned to play professionally with the Washington Bullets in the 1980s, his political plans were far enough along for teammates to nickname him "Senator."

McMillen won his first campaign for the House in 1986, edging out Republican Robert R. Neall. Since then, politicians say, McMillen has used the advantages of incumbency to establish a relatively firm grip on the 4th District.

"It's the little stuff that counts, and Tom is good at that," said state Sen. Michael J. Wagner (D-Anne Arundel). "He sends out lots of mail. He holds community meetings all over. He shows up for every ground-breaking, ribbon-cutting and baby-kissing.

McMillen is particularly proud of an agreement to create a 7,600-acre wildlife preserve with land that is now a part of Fort Meade in Anne Arundel County. He has also lobbied for money for a biotechnology research center in Baltimore.

On national and international issues, he has compiled a relatively liberal record, getting generally high marks from the American Civil Liberties Union and the political arm of the AFL-CIO. But he occasionally displays conservative leanings, such as his vote this summer in favor of a law banning flag burning.

Although still relatively low in seniority, McMillen has garnered sought-after committee assignments, serving on the Banking Committee until he moved to the Energy and Commerce Committee in February. Both panels put him in the middle of major policy debates, but both have caused him political problems in his district.

McMillen was attacked by environmentalists last spring for several votes on a landmark clean air bill, which is pending. They alleged that he sided with the auto industry in several cases to please Energy and Commerce Chairman John D. Dingell (D-Mich.), who helped get McMillen on the committee. McMillen says that the overall bill is good and that environmentalists wanted too many restrictions on car makers in some cases.

McMillen's tenure on the Banking Committee provides the basis for Blum's campaign against him. Blum has pointed out that while McMillen regulated the nation's financial institutions, he took $24,000 in campaign contributions from the savings and loan industry and $100,000 from other financial service companies.

"I'm not saying that Tom McMillen is corrupt," Blum said. "I'm saying his conduct is not in the public interest. It's not appropriate for a guy who is writing legislation that affects an industry to be asking the industry's lobbyists for money at the same time."

McMillen says there is no link between his campaign contributions and his votes on banking regulation. He says he has supported some legislation opposed by the industry.

Blum, 49, has spent most of the last 25 years working on Capitol Hill, but is making his first campaign for public office. He worked as a lawyer for several Senate committees, investigating subjects as diverse as housing fraud and the alleged drug connections of Nicaragua's contra rebels.

Blum says that, if elected, he would support higher taxes on upper-income taxpayers to help eliminate the federal deficit.