Sen. Olympia Snowe (R-Maine) has been flexing her muscle with Senate Democratic and Republican leaders this week, assisting both sides in winning battles over the $410 billion omnibus spending bill.

By threading the partisan needle, Snowe managed to help her fellow Republicans score votes on 13 more amendments than they had been already granted, while winning concessions from her own leadership to make sure the bill would not be completely blocked.

“I think there’s a case to be made to protect minority rights,— Snowe said in an interview Friday. “Majority rules, but you have to respect minority rights.—

Snowe said she called Majority Leader Harry Reid (D-Nev.) on Thursday night to say she could not give him her vote to bring debate on the omnibus to a close. Minority Whip Jon Kyl (R-Ariz.) had asked her to hold out in order for more Republicans to offer amendments. The Senate has already voted on 12 GOP-sponsored proposals to change the omnibus.

“I didn’t think eight to 10 more amendments was an unreasonable request,— said Snowe, who explained that she was operating out of a sense of fairness and of fostering bipartisanship.

“Frankly, it only builds a sturdier relationship between the two sides,— she added.

Snowe said she would support the bill on final passage and made clear to Kyl that she would only help Republicans “as long as it wasn’t going to be used to obstruct passage of the bill.—

One Republican leadership aide said Snowe is holding true to a letter that she signed last fall — along with every other GOP Senator — that cautioned Reid against trying to limit GOP amendment votes.

“Republican Senators appreciate that Sen. Snowe is someone who looks out for her constituents first but also is committed to allowing her colleagues the opportunity to offer their ideas, even if she ultimately disagrees,— the aide said.

Snowe would have likely been the 60th vote that Reid needed to end debate on the bill and kill an attempted GOP-led filibuster. With Democratic Sens. Evan Bayh (Ind.) and Russ Feingold (Wis.) defecting, Reid needed votes from four Republicans to win the procedural vote. Three other Republicans — Sens. Thad Cochran (Miss.), Kit Bond (Mo.) and Richard Shelby (Ala.) — appeared poised to help bring debate on the bill to a close.

However, Snowe was not the only Republican swayed by the minority rights argument. Democrats had been seeking the votes of a handful of other GOP Senators as well. They all took the same position, and several of them called Reid with a similar message Thursday night.

But Snowe’s posture is significant given that she is considered — along with her home-state colleague, Susan Collins (Maine) — one of the likeliest Republican Senators to vote with Democrats against GOP filibusters.

On election night in November, Reid confidently predicted Snowe and Collins would regularly be on Democrats’ side.

“They’re not going to be able to filibuster now,— Reid said. “We have a few Senators from Maine, and we’re going to have John McCain, who’s never been a filibusterer.—

Snowe clearly used that assumption to her advantage Thursday, just as Collins did when she played a pivotal role in negotiating a compromise on the $787 billion economic stimulus bill last month.

In the short term, Snowe’s move Thursday night not only forced Reid to extend debate on the bill, but also pass a stop-gap spending bill that would keep the government funded until Wednesday night. Snowe and a few other Republicans support passing the omnibus because it would give new program authority to federal agencies that have been operating under old authorities since last fall under a separate continuing resolution.