WASHINGTON - An hour before her colleagues gathered for their first vote of a new Congress, Sen. Kelly Ayotte slipped into an empty Senate chamber to savor the grandeur of her legislative home. As Ayotte, a freshman Republican from New Hampshire, sat down at the wooden desk where generations of lawmakers from her state had cast their votes, a doorman marched toward her with purpose.

The desks, he sternly told her, were for senators only.

Ayotte's induction that January day in 2011 into the most rarefied ranks of the nation's political class - female senators - had begun.

"The desk thing really stuck with me," Ayotte said. "There still just aren't that many of us."

In the 90 years since Rebecca Felton of Georgia became the first woman in the U.S. Senate - sworn in for a mere 24 hours - women remain an anomaly in the upper chamber. But with 20 female senators now in office - an all-time high - women have morphed from the curiosity they were for much of the 20th century into an important new force on key committees and legislation.

A record nine women now lead committees, including some of the most powerful. For the first time there is a woman - Sen. Barbara A. Mikulski, D-Md. - in charge of the Senate Appropriations Committee, which dispenses billions of dollars annually throughout the government and has long been dominated by men. Sen. Patty Murray, D-Wash., is the first chairwoman of the Budget Committee and is charged with shaping the Democratic strategy in the fiscal battle dominating Capitol Hill.

'GROWING IN POWER'

One of the biggest bills to pass the Senate last year was farm legislation led by Sen. Debbie Stabenow, D-Mich., who presides over the agriculture committee. Sen. Barbara Boxer, D-Calif., who is chairwoman of the Environment and Public Works Committee, shepherded the highway bill.

"We are growing in number," said Sen. Amy Klobuchar, D-Minn. "But more importantly, we are growing in our power. When I first started just six years ago, it was unusual to have a woman managing a bill."

Just as important, even male senators say, is the potential the women hold for changing the tenor of the Senate and pushing for compromise in the highly partisan atmosphere on Capitol Hill.

"I don't want to generalize, because this isn't true of all of them, but they tend to be interested in finding common ground," said Sen. Rob Portman, R-Ohio. "So I think it's going to have, and is having, a positive impact on the Senate."

BUILDING COALITIONS

While partisan division is the central characteristic of the modern Congress, women have begun to crack away at the gridlock by forming coalitions that have surprised leaders of both parties. Sen. Kirsten E. Gillibrand, D-N.Y., and Sen. Susan Collins, R-Maine, led the repeal in the Senate of "don't ask, don't tell" in 2010, allowing gay men and women to serve openly in the military.

This year, all four of the female Senate Republicans split with their party and voted with Senate Democrats to reauthorize the Violence Against Women Act, which had lapsed during the last Congress.

Politics remain just beneath the surface, however. In a recent roundtable involving the women and ABC's Diane Sawyer, Sen. Elizabeth Warren, D-Mass., sharply disagreed with Collins on the efforts the women should devote to reproductive rights. After Collins described reproductive issues as "settled law" and said, "I don't know why we would want to keep bringing those issues up," Warren shot back that "I don't think they are entirely settled" and that "we better speak out" when there are attempts, for example, to limit health insurance coverage for birth control.

BIPARTISAN DINNERS

On a practical level, the women's growing ranks have overtaken the physical facilities available to them. There are, at present, a mere two women's bathroom stalls near the Senate floor, which often means long lines. But the senators have learned to use the situation to their advantage: Stabenow said recently that she and Sen. Heidi Heitkamp, D-N.D., spent their time in the bathroom line strategizing over how they might get a new farm bill passed.

Off hours, the Senate women have a bipartisan dinner together once a month, a ritual organized by Mikulski, which they say creates personal bonds and helps them work together on policy.

At a recent dinner at the Capitol Hill home of Sen. Mary L. Landrieu, D-La., the women nibbled on bread pudding for dessert while they talked about children and, Landrieu said, "about how our siblings keep us in our places." She added, "It's just so nice to be able to relax and put your guard down."

The dinners "are the only reason I've been successful," Gillibrand said, recounting how Sen. Lisa Murkowski, R-Alaska, had helped her write the bill that provided health care to the first responders to the attacks of Sept. 11, 2001.

"In the Senate you have to start with a bipartisan core to get things done, and that core is often formed with the women," Gillibrand said.

Women have also focused on legislation that men do not typically consider, like financial security for women, an issue championed by Sen. Kay Bailey Hutchison, the Texas Republican who retired in January.

The seven women now serving on the Senate Armed Services Committee have begun to push their priorities, including efforts to prevent and adjudicate sexual assault in the military and to open combat jobs to women.

During the reauthorization of a bill to finance the military last year, Gillibrand went to the floor with an amendment to expand coverage for beneficiaries' children who have autism and other developmental disabilities, financed by a $45 million, one-year payment out of an existing military budget line.