WASHINGTON (AP) - Acting on a last-minute decision by President Clinton, the United States signed a treaty Sunday creating the world's first permanent international war crimes tribunal to bring to justice people accused of crimes against humanity.

The president said his action, taken with some reservations, builds on U.S. support for justice and individual accountability dating to American involvement in the Nuremberg tribunals that brought Nazi war criminals to justice after World War II. "Our action today sustains that tradition of moral leadership," he said.

The treaty should not be submitted to the Senate for ratification until certain concerns are met, he said.

"I believe that a properly constituted and structured International Criminal Court would make a profound contribution in deterring egregious human rights abuses worldwide...," the president said in a statement issued at the White House.

The treaty must be ratified by the Senate before U.S. participation in the tribunal becomes final. Fierce opposition to its terms is expected from conservatives led by Sen. Jesse Helms, R-N.C. Helms angrily responded Sunday that "this decision will not stand."

The president said he acted "to reaffirm our strong support for international accountability and for bringing to justice perpetrators of genocide, war crimes and crimes against humanity."

"In signing, however, we are not abandoning our concerns about significant flaws in the treaty," the president said. "In particular, we are concerned that when the court comes into existence, it will not only exercise authority over personnel of states that have ratified the treaty, but also claim jurisdiction over personnel of states that have not.

"Given these concerns, I will not and do not recommend that my successor submit the treaty to the Senate (for ratification) until our fundamental concerns are satisfied," he said.

David J. Scheffer, the U.S. Ambassador at large for war crimes issues, signed the treaty on behalf of the United States a few hours after Clinton authorized him to do so.

U.S. Secretary-General Kofi Annan issued a statement praising the U.S. decision, saying he was "well aware of the difficulties" Clinton faced and congratulating "him on his courage and far-sightedness in overcoming them."

Annan said the court "represents no threat to states with an organized criminal justice system. On the contrary, it is designed only to protect those most vulnerable people whose own government, if they have one, is unable or unwilling to prosecute those who violate their most fundamental human rights."

In Atlanta, The Carter Center also commended Clinton and noted that the center's founder, former President Carter, had urged him to sign the treaty in a Dec. 20 letter.

"I think that President Clinton, in signing this treaty, has offered the hope of justice to millions and millions of people around the world by signaling United States' support for the most important international court since the Nuremberg tribunal," said Richard Dicker, associate counsel of Human Rights Watch. He called it "a very important symbolic act."

At the UN, meanwhile, the treaty was signed by a representative of the government of Iran.

Clinton acted at Camp David, the presidential retreat in western Maryland where he and his family are spending the last New Year's weekend of his administration.

Sunday was the deadline for countries to sign on to the international criminal court treaty and transmit it to United Nations headquarters in New York. After Sunday, ratification is the only way a government can express support for the treaty or associate itself with it.

The court would be the first permanent institution created specifically to try charges of war crimes, genocide and crimes against humanity. At present the United Nations has two specifically targeted and temporary war crimes courts in operation. One deals with suspects from the Bosnia-Herzegovina civil war of the early 1990s and the other with people implicated in atrocities during unrest in Rwanda in 1994.

Treaty supporters contend that a permanent international war crimes court is "the missing link" in the global legal system and say that over the past half century there have been many instances of war crimes and crimes against humanity that have gone unpunished.

For example, supporters note that no one has ever been held accountable for the alleged genocide in Cambodia in the 1970s when an estimated 2 million people were killed by the Khmer Rouge or for killings in such other countries as Mozambique, Liberia and El Salvador.

Support for a permanent international war crimes tribunal was first expressed in the years immediately after World War II. Interest in creating such a court has been voiced periodically ever since.

The United Nations contends that setting up temporary courts to deal with alleged war crimes in specific countries has been an inadequate response because unavoidable delays lead to such consequences as deteriorated evidence, escaped or vanished witnesses, and witness intimidation.

Some in the United States have expressed concern, however, that U.S. approval of such an international tribunal might subject American citizens to politically motivated prosecutions.

Helms, chairman of the Senate Foreign Relations Committee, has campaigned vigorously against the court. He has pledged to give top priority during the congressional session starting next week to passage of a bill that would bar U.S. cooperation with any such international tribunal.

"Today's action is a blatant action by a lame-duck president to tie the hands of his successor," said Helms, who said the "kangaroo court" would leave U.S. service personnel subject to prosecution.

"For two years the administration has tried in vain to secure additional protections for American citizens, but was rebuffed at every turn by our so-called allies," Helms said.

Helms also has tried to persuade Israel, which had also delayed its decision until the last minute, to reject the international court. Following Clinton's lead, Israel declared Sunday that it had decided to sign the treaty establishing the international war crimes court under the United Nations. The United States and Israel were among the handful of countries that did not sign the statute creating the treaty when it was issued in Rome in 1998.

Israeli Ambassador Yehuda Lancry signed the treaty at U.N. headquarters in New York late Sunday.

Four countries signed the treaty on Friday - the Bahamas, Mongolia, Tanzania and Uzbekistan - which brings the number to 139.

Twenty-seven have ratified it, and 60 are needed before the treaty can enter into force.

Human rights groups pushed Clinton on Friday to sign the treaty. Human Rights Watch said "history will look harshly on President Clinton if he fails to sign," and Amnesty International said Clinton's signature "will demonstrate U.S. support for the rule of law and for equal justice for all."

See also: United Nations Web site on International Criminal Court