A widely anticipated referendum on same-sex marriage in Maryland appeared a certainty Thursday, as an unofficial count of validated signatures submitted by opponents exceeded the required number.

As of late Thursday afternoon, 70,039 signatures had been validated by local elections officials, exceeding the 55,736 required to put the measure on the ballot, according to an ongoing “unofficial” tally on the Maryland State Board of Elections Web site.

State Elections Administrator Linda H. Lamone said the statewide count has not yet been certified but that it “will probably go up” by the time that happens.

If the numbers hold, Maryland voters will be asked in November if they want to uphold a law passed this year that allows gay nuptials. The measure, which was signed by Gov. Martin O’Malley (D) in March, narrowly passed the House of Delegates after falling short in that chamber the year before.

No state has ever approved a ballot measure allowing same-sex marriage, and both sides have been gearing up for months for the fight in Maryland.

Late last month, the Maryland Marriage Alliance, the group leading the effort to overturn the state’s same-sex marriage law, turned in more than twice the number of required signatures with a month remaining to gather them.

Not all signatures are being validated by elections officials. As of Thursday, more than 4,000 had been rejected.

As part of its campaign efforts, Marylanders for Marriage Equality announced Thursday that it had opened two offices and hired a number of key staff.