WASHINGTON -- In the world of hardball politics, it's rare to see a member of Congress stand up to party leadership. It's practically unknown for a freshman.

But Michigan Republican Rep. John "Joe" Schwarz did when he signed onto a letter with 50 GOP colleagues last month asking Republican Leader Tom Delay of Texas to resign his leadership post.

"It is absolutely unacceptable to be a witness and stand by and watch these events occur without acting," said Schwarz of Battle Creek. "It was time to elect a leadership that was going to be a permanent leader, a leadership that didn't have to deal with a lot of personal problems."

The letter went out on a Friday and by that Sunday Delay had stepped down as majority leader to clear his name of money-laundering charges in a Texas court. New leadership elections were held last week.

"He (Schwarz) can't abide unethical behavior," Craig Ruff, an analyst at Lansing-based Public Sector Consultants who has watched Schwarz for some 20 years. "He also doesn't live in fear, so that gives him a leg up on other politicians."

Maybe it's his years as a doctor (ear, nose and throat specialist) or his CIA intelligence work in Southeast Asia in the 1960s.

"The pressure is the pressure," Schwarz, 68, said of GOP and special-interest groups trying to influence his vote. "...You get lobbied in your office. You get lobbied on the (House) floor. You get lobbied in the district. It doesn't make any difference."

These days, Schwarz regularly finds himself at the center of a tug-of-war between Republican and Democratic interest groups, mostly because he is one of only two moderate Republicans in the Michigan delegation. The other is Rep. Fred Upton of St. Joseph, who also signed the Delay letter. Republicans have a 9-6 majority on the Michigan delegation.

One day, Right to Life of Michigan activists are howling about his support for stem cell research. The next, MoveOn.org, the Web-based liberal advocacy group, is mobilizing voters to encourage him to vote against President Bush's budget.

Schwarz describes his first year in office as a learning experience, noting that even 16 years in the state Senate didn't quite prepare him for the arcane rules of Congress.

"About 75 percent of what went on I could comprehend pretty easily, and the other 25 percent was more like What the hell was that?," said Schwarz.

Schwarz said he did figure out that the only way to make a difference in a chamber with 435 members is to specialize. He's already announced that he won't stay in Washington forever, mostly because of age.

"The best way to achieve influence is to become the expert on a topic important to the district," said Larry Sabato, a University of Virginia political science professor. "That's how the House works... Senators are generalists, House members, specialists."

Schwarz's specialty? He's used his medical background on health-care policy, whether it be taming skyrocketing costs through high-deductible health insurance plans or seeking to expand stem-cell research.

His other interest is the military. His biggest legislative victory last year was the work he put into saving the Michigan Air National Guard Base in Battle Creek from closure by the Pentagon.

Even a victory as sweet as that doesn't make for smooth sailing. Former state Rep. Timothy Walberg is challenging Schwarz in the August GOP primary. Walberg and a handful of other Republican candidates lost the 2004 primary to Schwarz.

Walberg said he's back because Schwarz isn't a good fit with his conservative district, which includes rural counties that border Indiana.

"I do not feel that Joe is representative of this district for the conservative, traditional-values majority that's here," said Walberg. "To Joe's credit, he never said he would be any different than he is. Joe Schwarz is a liberal, and I'm a conservative."

Democrats beg to differ.

"For anybody who thought he was going to be a moderate and vote against the Republican caucus, he's been a big disappointment," said Mark Brewer, chairman of the Michigan Democrat Party. "He's not really stood up to his caucus or the president on very many issues," including federal cuts to Medicare and Medicaid.

Wherever they place him politically, some observers agree that while Schwarz can be arrogant at times and never suffers fools gladly, he always is straightforward and intellectually curious.

"I think Joe has to be Joe," said Rep. Vern Ehlers, R-Grand Rapids. "That's what he's always done in the past, and that's why he's been a good member of Congress. He doesn't pretend to be something he isn't."