A federal appeals court in Boston rejected Thursday an attempt to block President Bush from launching an invasion of Iraq, but appeared to leave the door open to a later challenge if the United Nations Security Council fails to authorize military action.

“The case before us is a somber and weighty one,” 1st U.S. Circuit Judge Sandra Lynch, a Clinton appointee, wrote for the panel. “We have considered these important concerns carefully, and we have concluded that the circumstances call for judicial restraint.”

The case was brought by a number of active-duty soldiers, military families and 12 House Democrats who sought to bar Bush from ordering an invasion because Congress has not formally declared war on Iraq.

Taking note of the fast-paced diplomatic and political maneuvering surrounding the decision on Iraq, the court held that it was not the right time for the judicial branch to enter the fray. But the panel appeared to reserve the right to step in even though the two other political branches of government appeared to be acting in concert.

And in a footnote, the panel left the door open for later action by the courts.

“This conclusion does not necessarily mean that similar challenges would never be ripe for decision before military action began; we reiterate the case-specific nature of the ripeness inquiry. Here, too many crucial facts are missing,” the ruling said.

John Bonifaz, an attorney who brought the case, said that if the Security Council votes against a military strike, he would immediately file an emergency request with the court to rehear the case.

“This case is far from over,” Bonifaz said in a telephone interview after the court handed down its ruling. “We regard this as a significant ruling.”

The lawmakers, led by Reps. Dennis Kucinich (D-Ohio) and John Conyers (D-Mich.), and military families argued that the resolution passed by Congress in October authorizing force against Iraq improperly ceded Congressional power to the president and authorized military action under the auspices of the United Nations.

“For various reasons, this issue is not fit now for judicial review,” the court said. “For example, should there be an attack, Congress may take some action immediately. The purported conflict between the political branches may disappear.”

Bonifaz said that “this case is now in the court’s eyes not ripe. But if the U.N. does not vote to authorize this war and the president nevertheless proceeds, then we think we have new facts to proceed until it is ripe.”

“If the U.N. votes no, we intend to go back.”

Justice Department officials could not be reached for comment.