THE event held late last month in the penthouse of the lawyers Barry Skovgaard and Marc Wolinsky had all the trappings of a top-flight fund-raiser, with five-star finger foods, four-finger cocktails and three-term senators, as Charles E. Schumer, Democrat of New York, spoke — and everyone else listened. Even the address, 252 Seventh Avenue, had a patina of glamour, being the building where Katie Holmes holed up after dumping Tom Cruise.

The only thing missing that evening was the guest of honor, another woman locked in a battle with a powerful man: Tammy Baldwin, the Democratic congresswoman who is running neck and neck with the longtime Republican lion Tommy Thompson for a United States Senate seat in Wisconsin. Scheduled to speak, Ms. Baldwin (who, like the hosts and many of the people in that room, is openly gay) was instead back home to respond to a sharp-elbowed new ad from Mr. Thompson, something that demanded the candidate’s presence in Wisconsin, and not amid fawning followers in a Chelsea loft.

And it is that just that balancing act — being a loyal, hard-working representative of her home state and an emerging national figure in the gay community — that has Ms. Baldwin, 50, on the edge of making history, and her supporters, including some of nation’s most important gay donors, on the edge of their seats.

Though a victory by Ms. Baldwin on Tuesday would represent the election of the first openly gay or lesbian person to the Senate, gay groups have been surprisingly low-key about their public support. Fund-raisers have largely been intimate affairs at people’s homes; no giant fund-raising galas in gay enclaves like West Hollywood or the Castro in San Francisco. There have been no celebrity onslaughts like those unleashed in the federal court fight against Proposition 8 (California’s same-sex marriage ban).