WASHINGTON >> After a pair of votes the other day on some fine points of a major financial regulatory bill, Sen. Scott Brown of Massachusetts ducked out of the Capitol and back to his office, where he traded his suit and tie for softball gear, to lead his staff in an afternoon match-up against the office of Sen. Lamar Alexander of Tennessee.

The Brown team uniform was a T-shirt proclaiming “;Great Scott”; on the front. On his back, the team captain wore No. 41—a continuing badge of pride for the improbable victory in January that made him the 41st Republican in the Senate and stripped Democrats of the 60th vote they needed to surmount filibusters and advance their agenda unchecked.

Four months after being elected to fill the seat of the late liberal lion Edward M. Kennedy and becoming a national hero to conservative Americans, Brown still has an air of celebrity about him. But a pinup boy for the Tea Party he is not.

In his first vote after taking office, Brown joined with Democrats, and their majority leader, Harry Reid of Nevada, in support of a $15 billion jobs bill. He was the first of just five Republicans to break with the party's leadership on that bill.

And although he kept his campaign promise to oppose the big health care legislation, and has voted with the Republican leadership in the overwhelming majority of cases, he has also sided with Democrats on some important issues. Most notably, he voted in favor of the financial regulatory bill even though the Senate Republican leader, Mitch McConnell of Kentucky, and the rest of the conference leadership voted no and denounced the measure as overly expanding the government.

“;Listen, I have always said I don't work for Mitch McConnell and I don't work for Harry Reid, I work for the people of Massachusetts,”; Brown said in an interview. “;I am not quite sure what all the surprise is, and people wondering kind of like, 'wow, he's independent.' I have always been this way. I am going to look at each and every bill and look at the merits of it.”;

But his willingness to team with Democrats is already raising eyebrows and ire among some voters in Massachusetts who backed his candidacy. They say he is betraying some of the conservative ideals that he espoused during the campaign—especially in his vote on the financial regulation bill.

“;People are disappointed in this vote, because we see it as contrary to limited government and supporting free markets,”; said Christen Varley, the leader of the Greater Boston Tea Party. “;I think people are realizing that in some situations Senator Brown will be an ally and in some he will not. Some people are angry. Some people are disappointed but willing to wait and see what happens with the next votes.”;

Varley said she was urging Tea Party members to contact the senator's office and express their disappointment but also counseling them to develop a healthy sense of pragmatism, especially in a state as traditionally liberal as Massachusetts.

In the pattern of his votes, it is already clear that Brown has joined the small club of centrist Northeast Republicans that by the start of this year had shrunk to two members: Sens. Olympia J. Snowe and Susan Collins of Maine.

And while incumbents in traditionally Republican states in the South and the West are facing serious pressure from the right, Brown could soon be joined in the Senate by like-minded Republicans from other regions, including Rep. Michael N. Castle, who is running for Senate in Delaware, and Rep. Mark S. Kirk, who is running in Illinois.

“;I tease my colleagues from the South, that it is the Northeastern Republicans that are the resurgence of the Republican Party and leading our party back out of the wilderness,”; Collins said in an interview. “;And because they are more centrist,”; she added, “;They have an excellent chance of prevailing.”;

Already, Brown is discovering that working across both sides of the aisle can be perilous or, as Collins put it, “;an uncomfortable role.”;

After Brown opposed an initial effort by Democrats to close debate on the financial regulatory bill, Reid, the majority leader, was incensed. And although he did not mention Brown by name, it was abundantly clear that Reid was talking about the Massachusetts Republican when he said after the vote, “;a senator broke his word.”;

Brown accepted responsibility for what he described as a misunderstanding that led Reid to believe Brown would vote to end debate when he was still working to address issues of concern to Massachusetts.

Brown chalked it up to a communication breakdown that could have been avoided with a face-to-face chat.

“;It was a good lesson to me,”; he said. “;Just knock on his door.”;

Republican leaders accept that Brown will not always hew to the party line.

“;A Massachusetts Republican and a Mississippi Republican and a Florida Republican and a Colorado Republican aren't going to think the same on all things,”; Alexander, the No. 3 Senate Republican, said in an interview on C-Span's “;Newsmakers.”;

But Alexander said that in a broader sense, there is cohesion.

“;On one issue I think Republicans are unified,”; he said. “;That is, too much debt, too much spending, too many taxes and a need for a check and a balance on what we see is an overreaching government in Washington. I think Scott Brown was elected partly for that reason.”;

Colleagues describe Brown as genial and easy to work with. Republicans say he speaks up in conference meetings a bit more than most freshman senators but not in a way that oversteps. Democrats say he has been willing to be collaborative.

Sen. Charles E. Schumer, D-N.Y., said he and his staff were recently invited to a Friday afternoon “;happy hour”; on the terrace of Brown's office.

“;If you had to pick from a handful of Republicans who you can work with and who will be predisposed to do something together,”; Schumer said. “;He is one of them.”;

Political reality suggests that Brown must now position himself in the center if he hopes to be re-elected. On Thursday, in the Armed Services Committee, he voted against repealing the “;don't ask, don't tell”; law that bars gay men and lesbians from serving openly in the military—a stance certain to anger some voters in Massachusetts, where gay marriage is legal.

“;I'm a fiscal hawk and a security hawk,”; Brown said. “;On the other issues I am going to look at every one of them and make a decision accordingly.”;