Calling Senator Clinton “a complete disappointment” because of her opposition to same sex marriage, the director of an influential gay rights organization told associates he will not participate in a fund-raiser hosted by several of her gay supporters.

The refusal by the director of Empire State Pride Agenda to lend his name or raise money for the March 10 fund-raiser set marriage equality as a new benchmark for candidates seeking political support from the gay community.

Other gay advocates said Mrs. Clinton has been a leader on other issues of concern to gay voters, and her position on marriage should not disqualify her from their support.

In an e-mail to board members earlier this month, ESPA’s Alan Van Capelle said he still supports Mrs. Clinton’s reelection,”despite her regrettable state ments” on same-sex marriage and her support of the so-called Defense of Marriage Act.

But he said supporting next month’s fund raiser,organized by prominent gay Clinton supporters including the City Council president, Christine Quinn, “will actually hurt our community.”

“It will send a message to other elected officials that you can be working against us during this critical time and not suffer a negative pushback from the gay community,” Mr. Van Capelle wrote.

An ESPA spokesman, Joe Tarver, said the organization would have no further comment on Mr. Van Capelle’s e-mail, which was sent February 10 and marked “confidential.” But, Mr. Tarver added, “We are being overwhelmed by positive e-mails and phone calls around the country about Alan’s views on this. We think we’ve touched a nerve on something.”

Mrs. Clinton opposes same-sex marriage but supports civil unions, which confer many of the same benefits to gay couples.

Her position mirrors that of her colleague, Senator Schumer, but puts her at odds with other prominent Democrats running statewide in New York this year. Among them is the attorney general, Eliot Spitzer, a candidate for governor, who said he would support legislation legalizing gay marriage if elected.

Mrs. Clinton also supports the Defense of Marriage Act, a 1996 federal law signed by her husband that defines marriage as “a legal union of one man and one woman as husband and wife.” She opposes a Constitutional amendment banning same-sex marriage, which many gay rights advocates cite as their most pressing political concern.