HARRISBURG -- Legislation to outlaw same-sex marriages in Pennsylvania appeared to take a step forward yesterday, but some proponents of the ban claimed it was actually a step backward.

The Senate Judiciary Committee approved a bill that would change the state constitution to prevent same-sex marriages. But the panel also amended the bill, eliminating a key provision that was in the version the House approved last week.

Conservatives who oppose gay marriage said the Senate panel's amendment seriously weakened the bill.

"I am disappointed," said Pennsylvania Family Institute President Michael Geer, claiming the amendment "may be an effort to kill the bill."

He feared the Senate panel's action could delay final approval of the bill by the full House and Senate. Backers are hoping both will approve an identical bill by June 30.

If they don't, a required public notice of the proposed constitutional change can't go out in early August, 90 days before the November election. And that means final approval by statewide voters couldn't happen by November 2007, as advocates are seeking.

The House-passed bill had outlawed both actual marriages between gay people and a newer procedure called civil unions. The bill describes such unions as living arrangements that are "substantially equivalent to that of marriage for unmarried individuals."

With civil unions, also called domestic partnerships, a couple, usually of the same sex, agree to live faithfully with each other and share resources.

Civil unions are not currently recognized under Pennsylvania law.

"They are committed relationships between two people," said Stacey Sobel of the Center for Lesbian and Gay Civil Rights in Philadelphia.

The couple doesn't receive an actual marriage license but does register with the state and receive a document acknowledging the partnership, she said.

The concept began in Vermont in 2000 as an effort "to provide marriage equality for same-sex couples without being called married or having a marriage license," said Larry Frankel, legislative director for the Pennsylvania branch of the American Civil Liberties Union.

Civil unions are sometimes formed by an elderly man and elderly woman who live together but don't want to get married, Ms. Sobel said. Connecticut adopted civil unions in 2005, and several European countries permit them.

"Civil unions have all the same rights and responsibilities as marriage" but without a marriage license, she said.

The amendment to delete the ban on civil unions was sponsored by Sen. Jane Earll, R-Erie, and approved 9-5 by the committee.

Mr. Geer said he is concerned that gays might try to evade legal prohibitions on same-sex marriage by simply calling their partnerships civil unions. He said Pennsylvania should be proactive in banning both gay marriage and civil unions.

Rep. Daryl Metcalfe, R-Cranberry, also objected to Mrs. Earll's amendment, which he said watered down the bill.

"I want to protect marriage and ensure it remains between one man and one woman. I object to deleting the ban on civil unions," he said.

Mrs. Earll claimed that references in the bill to civil unions just make the legislation confusing to voters. She said it's unnecessary to outlaw civil unions when they don't even exist in Pennsylvania.

"We're fighting hypothetical ghosts here," she said.

Mrs. Earll said the amended bill now reads the same as the 1996 Pennsylvania Defense of Marriage Act, stating that "a marriage is only between one man and one woman." She contended that is sufficient wording.

Sen. Jane Orie, R-McCandless, opposed the amendment, saying "it derails the purpose of this bill," which is to "protect the sanctity of traditional marriage" and outlaw gay marriages or unions of any kind.

The amended bill now moves to the full Senate for action, perhaps as early as Monday. Gay marriage foes may try to change the wording back to the way the bill read in the House.

To change the state constitution, an identical bill must pass the House and Senate in two consecutive sessions, and then be approved by voters in a statewide referendum. The soonest that could happen would be November 2007.

Opponents of gay marriage want the Senate to approve the version of the bill that the House approved so that the required 90-day notification of the constitutional change can be given to voters in early August.

Groups that oppose bans on gay marriage, including the American Civil Liberties Union and the Center for Lesbian and Gay Civil Rights, reacted cautiously to the amended bill.

Mr. Frankel said he doesn't want the Legislature to outlaw either gay marriage or civil unions, but saw the change made yesterday as a small improvement. He said the controversial measure is being rushed through the Legislature without sufficient hearings.

Banning civil unions, he said, could hurt both same-sex and opposite-sex couples. He said the state shouldn't be wasting its time interfering in people's personal lives.

During the Judiciary Committee meeting, Sen. Barry Stout, D-Bentleyville, lashed out at his colleagues for spending valuable time on same-sex marriage, when important matters like the state budget and property tax relief need to be enacted.

"I am ashamed this committee is being used to divert attention from important issues," he said. "People are sick and tired of us not dealing with their legislative concerns."