Eight lawmakers and the Anne Arundel County court clerk are appealing a Baltimore judge's ruling that they cannot join the lawsuit as defendants.
The same-sex couples and the attorney general's office oppose the bid by the legislators and others, saying they have no role in defending the constitutionality of the Maryland law. They argue that it is the attorney general's job to defend state laws.
A bill calling for a constitutional amendment banning same-sex marriage is dying in the General Assembly. Its proponents, some of whom are the legislators trying to intervene in the court case, pledged to push for passage next year.
If allowed in, he said, the lawmakers can tie the case in procedural knots to delay reaching the real issue.
"If they are allowed to intervene, this case will be decided in the next millennium," said Andrew H. Baida, a lawyer for the gay couples.
But the lawmakers say they are neither grandstanding nor being obstructionist.
"We don't want to tie up the lawsuit. We want to establish that marriage is between a man and a woman," said Del. Herbert H. McMillan, an Anne Arundel Republican.
Nationally, it is rare for lawmakers to want to become parties in lawsuits. Legislators' bids in other states to become defendants in same-sex marriage cases have been denied.
The Maryland Court of Appeals, which is to hear arguments in the case today, has never ruled on the question.
The legislators, Anne Arundel County Clerk of the Court Robert P. Duckworth, who was running for Congress at the time, and a Baltimore woman asked to become parties in the lawsuit.
Judge M. Brooke Murdock ruled against them in September, without a hearing and before either the attorney general's office or the couples filed responses to their request. They appealed.