They will be evaluating the effort against last year’s wildly successful drive to challenge the law allowing some illegal immigrants to pay in-state tuition rates. And the traditional marriage group’s progress will be measured against its self-imposed goal of producing 150,000 signatures by the end of June.

“The reality is there is incredible excitement out there,” said Derek McCoy, executive director of the Maryland Marriage Alliance and pastor of aPrince George’s Countychurch. “I don’t think there is anything that has hit Maryland like this in years.”

By Thursday, the group has to submit a third of the 55,736 signatures needed to petition a law to referendum, or 18,579. McCoy says the campaign will have more than twice that and will deliver the names Tuesday, two days early. After that, the law’s opponents have until June 30 to submit the balance of the names.

Supporters of same-sex marriage say the pace seems to be slower than anticipated — and believe a recent string of high-profile endorsements for their cause are helping to swing public opinion to their side.

“We are seeing signs that they are having more trouble than they expected,” said Josh Levin of Marylanders for Marriage Equality, a gay rights group that is preparing to defend the state’s new marriage law. But Levin quickly added that he has “no doubt” the law’s opponents will succeed in putting it before the voters.

Supporters of the law argue momentum started picking up when President Barack Obama this month announced his support for same-sex marriage. Former Secretary of State Colin Powell said in a TV interview that he’s in favor.

And the NAACP, the country’s oldest civil rights group, voted to endorse the right of gays to marry. The national civil rights group will provide on-the-ground help in Maryland if requested by the local branch, a spokesman said.

New automated polling results — albeit from the gay rights group — show a substantial increase in support for the Maryland law among African-Americans, who make up about a quarter of the state’s registered voters and are expected to turn out in high numbers this fall to support Obama. The poll numbers track recent national independent surveys on same-sex marriage.

Maryland’s legislature passed the law legalizing same-sex marriage in March, but it does not go into effect until January 2013. The date was chosen to give opponents time to put the measure on the November ballot.

McCoy says he has no concerns about the pace of signature gathering or flagging enthusiasm. Any perceived sluggishness, he said, is likely due to the rigorous method his group uses to check the petition forms before accepting them. He estimated that several thousand signatures have been rejected and won’t be counted.

Completed and verified petitions are whisked away from the group’s Hanover headquarters and stored in a steel vault. (McCoy would not say where it is — though he provided photos.)

In Bel Air last week, a steady stream of people approached a table set up by a trio of Maryland Marriage Alliance volunteers outside a Motor Vehicle Administration office. The venue provides a ready supply of people who have to wait around. Those trying to repeal the immigration law used the same method last year.

“Where do I sign up?” was the only question from Donald Johnson, a 76-year-old, born-again Christian who drove his pickup truck to the MVA for the express purpose of signing the petition.

Like most others observed at the site by a reporter, Johnson needed no pitch, explanation or convincing. “I have several nieces and nephews who are homosexual,” he said. “I don’t approve of their lifestyle.”

The Maryland Marriage Alliance started its signature-gathering effort in churches, but has broadened the campaign to include door-knocking as well as stands at festivals and the MVA offices. The organization is not overly hierarchical: One activist in Allegany County took it upon himself to have 17,000 blank petitions inserted in theCumberland Times-News and delivered to Maryland households.

“People are sending those in to us,” McCoy said. “We are getting Western Maryland, one by one by one.”

Still, most of the people who signed the petition Wednesday at the MVA office mentioned religion and said they heard about the drive at their church.