SACRAMENTO, CALIF. ? Holding to his pledge, Gov. Arnold Schwarzenegger on Thursday vetoed landmark legislation to legalize same-sex marriage in California.

Walking a political tight-rope, the governor vetoed the same-sex marriage legislation, as expected, but he also embraced four other measures broadening rights for domestic partners.

Advocates on both sides of the hot-button issue said the governor’s veto pen did little to settle a fierce, ongoing debate that is expected to intensify next year with two new initiatives in the works to restrict marriage to a man and a woman.

“This was the big enchilada and it’s very disappointing,” said Patrick Soricone, executive director of the Billy DeFrank LGBT Community Center in San Jose. But, he added, “the struggle for civil rights and equality kind of never goes away.”

Schwarzenegger objected to the same-sex measure authored by Assemblyman Mark Leno, D-San Francisco, “because I do not believe the Legislature can reverse an initiative approved by the people of California,” he wrote in his veto message. The governor was referring to Proposition 22, which defined marriage as a union between a man and a woman and passed in 2000.

The measure amended the California Constitution and therefore cannot be changed without a vote of the people, the governor said. Leno’s bill does not call for such a vote. In addition, the proposition is under court challenge as unconstitutional.

“This bill simply adds confusion to a constitutional issue,” Schwarzenegger wrote. “If the ban of same-sex marriage is unconstitutional, this bill is not necessary. If the ban is constitutional, this bill is ineffective.”

Leno and other supporters of his legislation found the governor’s decision tough to take. They called on him to oppose next year’s initiatives. Leno’s bill was the first legalizing same-sex marriage to pass any legislature in the nation, without a court order involved, and thrust California into the national spotlight.

“The governor has failed his test of leadership and has missed a historic opportunity to stand up for the basic civil rights of all Californians,” Leno said. “He cannot claim to support fair and equal protection for same-sex couples and veto the very bill that would have provided it to them.”

Democrats portrayed same-sex marriage a civil rights issue, while Republicans pointed to Proposition 22. The explosive question may serve as a campaign issue next year as well. Both Democratic candidates for governor – Treasurer Phil Angelides and state Controller Steve Westly – issued statements condemning the veto.

Art Torres, the chairman of the California Democratic Party, said the governor had “bowed to pressure from the extreme right and shown just how narrow his thinking is.”