BALTIMORE (AP) – Maryland’s highest court Tuesday upheld a state law defining marriage as a union between a man and a woman, ending a lawsuit filed by same-sex couples who claimed they were being denied equal protection under the law.

A divided Court of Appeals ruled that Maryland’s 1973 ban on same-sex marriage does not discriminate on the basis of gender and does not deny any fundamental rights, and that the state has a legitimate interest in promoting opposite-sex marriage.

The decision essentially sent the same-sex-marriage issue back to the legislature, where lawmakers on both sides of the debate predicted a flurry of activity in the next session.

“Our opinion should by no means be read to imply that the General Assembly may not grant and recognize for homosexual persons civil unions or the right to marry a person of the same sex,” Judge Glenn T. Harrell Jr. wrote for the four-judge majority, which also included Judges Dale R. Cathell, Clayton Greene Jr. and Alan M. Wilner.

Chief Judge Robert M. Bell and Judge Lynne A. Battaglia dissented. Judge Irma S. Raker wrote a separate dissent but also concurred with the majority, in part.

“It was a close case. We knew it was going to be close,” said Assistant Attorney General Robert Zarnoch, who argued the case for the state. The attorney general’s office maintains that the legislature, not the court, should decide the legality of same-sex marriage.

“It wasn’t a slam-the-door kind of argument,” Zarnoch said. “We were just saying it was not in the right place.”

But plaintiffs in the lawsuit said the judges missed an historic opportunity to strike down a discriminatory law.

“I think history will hold them in contempt,” plaintiff Lisa Polyak said of the judges. “To create a legal solution in a vacuum that doesn’t recognize that the constitution is there to support the people is to create an ignorant and irrelevant solution.”

The decision, however, had precedent in other states. According to the Marriage Law Foundation, a nonprofit group that defends heterosexual marriage and tracks such cases, more than 20 American appellate courts have rejected the argument that limiting marriage to opposite-sex couples is unconstitutional.

“It’s another in a long string of sensible, defensible, correct judicial decisions,” said Monte N. Stewart, the foundation’s president.

The ruling was certain to revive the same-sex-marriage debate in the State House. Delegate Don Dwyer, R-Anne Arundel, said he plans to introduce a constitutional amendment banning same-sex marriage as “insurance to make sure this will not come up again in the future.”

Such an amendment is unlikely to go anywhere in the heavily Democratic legislature and Gov. Martin O’Malley would oppose it, according to his spokesperson, Rick Abbruzzese.

“The governor supports civil unions,” Abbruzzese said. “He thinks that civil unions is a reasonable compromise.”

In a statement, O’Malley said he respected the court’s decision.

“As we move forward, those of us with the responsibility of passing and enforcing laws have an obligation to protect the rights of all individuals equally, without telling any faith how to define its sacraments,” O’Malley said.

Sen. Richard Madaleno, D-Montgomery, who is gay, said he plans to introduce a bill to allow same-sex marriage. He also expects a proposal to create civil unions.

“I think we’ll have a lengthy discussion next session about what the options are for legal recognition for gay people,” Madaleno said.

Many of the plaintiffs in the lawsuit have children, and they argue that their families are being denied the stability and legal protection that comes from having married parents.

Lisa Kebreau, 39, and her partner, Mikki Mozelle, 31, who live in Riverdale, have three children, ages 17, 2 and 20 months.

“We really wanted them to understand how normal and good their family is – that their family is just like any other family,” Kebreau said.

Nine same-sex couples and a gay man whose partner died filed a lawsuit in 2004 against court clerks who denied their applications for marriage licenses. Baltimore Circuit Judge M. Brooke Murdock in January struck down the law defining marriage as a union between one man and one woman, but the state immediately appealed.

Murdock’s ruling was put on hold during the appeal and never took effect – unlike in Iowa, where same-sex marriage was legal for less than 24 hours last month. Massachusetts is the only state where same-sex marriage is legal, but nine other states have approved spousal rights in some form for same-sex couples – California, Connecticut, Hawaii, Maine, New Hampshire, New Jersey, Oregon, Vermont and Washington.

Plaintiffs in the Maryland lawsuit said they would lobby the legislature for full marriage rights and would not be satisfied with civil unions, which they compared to Jim Crow laws.

“It’s a separate system. And separate is never equal,” said Gita Deane, who has been Polyak’s partner for 26 years.

Said Polyak: “It’s telling us to drink from another water fountain.”