Three gay couples filed a lawsuit Tuesday seeking to strike down Minnesota’s ban on gay marriage and add the state to the growing list of those allowing same-sex couples to get legally married.

The lawsuit in Hennepin County District Court is an attempt to overturn Minnesota’s 1997 Defense of Marriage Act. It asks for an order that county clerks begin issuing marriage licenses to same-sex couples.

Plaintiffs said they want the same rights as heterosexual married couples, the absence of which they said complicates a host of financial, medical, child-rearing and other important decisions.

“It’s a burden on a daily basis to not have the ordinary assumption of being married that everyone else has,” said Thomas Trisko, a plaintiff along with his partner of 36 years, John Rittman.

But the couples face significant legal hurdles, including a 1971 Minnesota Supreme Court decision that said since state law didn’t specifically authorize same-sex marriages, they were prohibited. The Defense of Marriage Act strengthened that ruling.

Opponents of gay marriage predicted the lawsuit could rally new support for the dormant effort to amend a same-sex marriage ban into the state constitution. Tom Prichard, president of the Minnesota Family Council, predicted it would be an issue in 2010 statewide elections.

“This is the latest evidence marriage is under assault in our legal and political community,” Prichard said in a news release.

The lawsuit contends the Defense of Marriage Act violated the “single subject” rule of the Minnesota Constitution and should be thrown out because it passed after it was amended to a larger health and human services bill in the state House. However, there have been few successful challenges based on single-subject grounds to laws passed by the Legislature.

Even if this one succeeds, judges would still have to reverse the 1971 state Supreme Court decision. Peter Nickitas, the attorney who filed the lawsuit, predicted the case would reach the current state Supreme Court, where most of the members were appointed by Gov. Tim Pawlenty, a gay marriage opponent.

But Nickitas said changing times would be a factor.

“The 1971 ruling took place in circumstances very different from ours and in a country very different from ours,” Nickitas said. He pointed out that in 2005, the U.S. Supreme Court struck down its own 1986 ruling allowing states to keep anti-sodomy laws on the books. The 2005 ruling was seen as a major victory for gay rights but was issued by a court considered more conservative than the one in 1986.

The states of Massachusetts, New Hampshire, Vermont and Iowa as well as the District of Columbia have legalized gay marriage either through legislative action or court ruling in recent years. New Jersey has civil unions, and Hawaii’s legislature passed a similar bill last month. Seven other states allow some type of domestic partnerships.

Minnesota Republicans are likely to make the lawsuit a campaign issue. But Nickitas said that wouldn’t sway his clients.

“In 1967, a majority of people opposed interracial marriages yet the Supreme Court of the United States did the right thing” by legalizing the practice nationwide, Nickitas said.

State Sen. Scott Dibble, D-Minneapolis, said he sympathized with the plaintiffs but worried their case lacked “a sufficient constitutional foundation” and would fail. Dibble, who is gay, said that could be an even bigger setback for gay marriage rights in Minnesota.