A pivotal case in the debate over gay marriage in New York is set to begin tomorrow in state Supreme Court, where a Christian legal group from Arizona will face off against representatives of the governor’s office in the first direct legal challenge to Governor Paterson’s executive order mandating that all state offices recognize out-of-state same-sex unions.

The Alliance Defense Fund is suing Mr. Paterson, citing an online dictionary’s definition of the word “marriage,” and claiming that legal recognition of such marriages “will undermine the democratic process and force taxpayer dollars to fund benefits for same-sex couples.”

Other plaintiffs in the suit include the state Assembly’s minority leader, James Tedisco, as well assemblymen Daniel Burling and Brian Kolb and senators Martin Golden and Serphin Maltese.

“This isn’t about morals or ethics, it’s about a legal standard in New York,” a lawyer for the Alliance Defense Fund, Brian Raum, said.

In May, Mr. Paterson issued the executive order directing state agencies to “ensure that terms such as ‘spouse,’ ‘husband,’ and ‘wife’ are construed in a manner that encompasses legal same-sex marriages.”

In the suit, the Alliance Defense Fund says the order was an illegal breach of the separation of powers, in that Mr. Paterson did not consult the Legislature about revising the legal status of those terms before issuing the order.

The suit also cites the online edition of the Merriam-Webster dictionary as evidence that the word “marriage” applies only to a bond between a man and a woman.

Currently, gay marriages cannot legally be carried out in New York State. However, same-sex marriages from places where they are legal — such as Massachusetts or Canada — have long been acknowledged by common law as legitimate unions in New York.

In 2006, the state’s highest court, the Court of Appeals, ruled that the state constitution did not require recognition of same-sex marriages and that any changes to their legal status would have to be decided by the state Legislature. However, it did not answer the question of whether the state would recognize out-of-state gay marriages.

A string of recent court decisions are on the governor’s office’s side, especially when it comes to provision of benefits.

In the past two years, the Alliance Defense Fund has tried unsuccessfully to challenge the state comptroller’s office, a Westchester county executive, and the state Department of Civil Services on their policies of recognizing gay marriage for services such as accidental death benefits.

A gay rights group, Lambda Legal, will be intervening in tomorrow’s hearing on behalf of a New York same-sex couple married in Canada. “This case is really just the Alliance Defense Fund piling on one more nuisance case, when the issue’s already been effectively passed over,” Lambda Legal’s litigator, Susan Sommer, said.