Hartford, Conn. ? The idea that civil unions could be a satisfying but less contentious substitute to gay marriage was knocked down Friday by Connecticut’s Supreme Court.

There is no substitute, the justices ruled 4-3 as they made the state the nation’s third to allow same-sex weddings.

The ruling might not have been as earthshaking as the one in Massachusetts that allowed gay marriage for the first time in the U.S., or the one in California that made it legal on the other side of the country and in the nation’s most populous state. But it cut into the view that there is some solid middle ground on an issue that has inflamed passions on both sides.

“It’s another court saying that separate but equal is not OK,” said Edward Stein, a professor at the Cardozo School of Law in New York City. “As state courts start to say this … gradually, over time, there might be a consensus that emerges.”

Same-sex weddings are expected to begin in Connecticut in less than a month. Out-of-staters will be eligible, but few other states are likely to recognize the unions.

The vast majority of states, including Kansas, ban gay marriage, but some have passed laws that recognize same-sex unions in some way.

The White House reacted to the ruling by again raising the prospect of a federal constitutional amendment defining marriage as between a man and a woman.

“It’s unfortunate that activist judges continue to seek to redefine marriage by court order without regard for the will of the people,” Karl Zinsmeister, President Bush’s domestic policy adviser, said in a written statement. “Today’s decision by the Connecticut Supreme Court illustrates that a federal constitutional amendment may be needed if the people are to decide what marriage means.”

The ruling cannot be appealed to federal courts because it deals with state constitutional issues, Connecticut Attorney General Richard Blumenthal said.