HARRISBURG — The stage is set for the full Pennsylvania Senate to vote on a constitutional amendment that would outlaw same-sex marriage and civil unions in the state, although chances appear slim it will gain traction in the House.

The Senate Appropriations Committee approved the measure in an 18-8 vote Monday after a 30-minute debate. Moments after it passed, more than 100 people rallied in the Capitol against the amendment.

Officials say a vote in the full Senate is possible as early as today's floor session. Approval by the Republican-controlled Senate would be the first step in a multiyear process that is required before a proposed constitutional amendment can be brought to voters in a statewide referendum.

The Senate action, however, may be largely symbolic. No similar bill has been introduced in the House, and Republican proponents of the measure say there is little chance of getting it through the Democratic-controlled chamber.

After the Appropriations Committee vote, opponents of the measure gathered in the Capitol Rotunda, hoisting signs and cheering legislators who showed up to speak against it.

Pennsylvania law already defines marriage as a union between a man and a woman, but proponents of the amendment, including religious and conservative values groups, say writing the ban into the constitution will prevent a judge from overturning the law or opening the door to civil unions between gays and lesbians.

Sen. John Gordner, R-Columbia, who spoke for the measure in the Appropriations Committee, insisted it is not intended to take away any rights, such as employer health care benefits, that some gays enjoy now. He added that no appellate court in the 18 other states that have approved similar language to this measure has taken away rights from gays.