By Joanne von Alroth
CHICAGO, Dec 28 (Reuters) - Illinois could become the next U.S. state to legalize gay marriage with a bill set to be introduced in the state Senate in early January, even before a new legislature takes office with a super-majority of Democrats in both houses.
Buoyed by November election referendum victories for gay marriage in Maryland, Maine and Washington state, gay marriage supporters in Illinois said they plan to press for approval in the Democrat-majority legislature. If it passes, that would make Illinois the tenth state to approve same sex nuptials.
Approval in President Barack Obama's home state would be a symbolic victory for gay rights activists after the president endorsed same sex marriage in May.
Chicago state Senator Heather Steans will introduce a gay marriage proposal next week, said Rikeesha Phelon, spokeswoman for Illinois Senate President John Cullerton.
"The Senate president and Senator Steans are confident they have the votes to pass a same-sex marriage bill," Phelon said.
Even if Illinois lawmakers fail to approve gay marriage before a newly-elected legislature takes office on Jan. 10, there is a reasonable chance of passage later in the year because Democrats gained seats in the November election and will have super-majorities in both chambers.
No Midwest state has approved gay marriage by a vote of its legislature. Iowa's Supreme Court ruled in 2009 that same sex marriage was legal, a decision some opponents have been trying to overturn ever since.
In June, 2011, Illinois legalized civil unions, which grant some of the rights of marriage to same sex partners. But gay rights activists said that did not go far enough.
All prominent Democrats in Illinois have endorsed gay marriage, including Chicago Mayor Rahm Emanuel and Governor Pat Quinn.
One issue to be resolved is whether Illinois should allow religious groups the option of declining to perform same-sex marriages. New York granted such an exception in 2011 in order to secure the legislative votes to legalize gay marriage there.
A bill introduced in the Illinois House, where support is not as strong as in the state Senate, offers such a religious exemption. Democrats hold a majority in the House too.
Last week, at least 260 Illinois faith leaders including representatives of several Jewish congregations and Protestant denominations, published a letter supporting same sex marriage.
"There can be no justification for the law treating people differently on the basis of sexual orientation or gender identity," the letter says.
But the Catholic Conference of Illinois, which represents Catholic bishops in the state, said on its website that marriage should be reserved for a man and a woman.
In addition to the three states which voted in November to legalize gay marriage, six others allow it - Iowa, Massachusetts, Vermont, New York, Connecticut and New Hampshire, plus the District of Columbia. (Writing by Greg McCune; Editing by Claudia Parsons)