UNITED NATIONS (Reuters) - Despite heavy U.S. opposition, the first permanent global criminal court to try individuals for the world's most heinous crimes is only four nations shy of becoming a reality.

As of Wednesday, 139 countries have signed a 1998 treaty to establish the International Criminal Court and 56 of them have ratified it. A total of 60 ratifications by national legislatures is needed for the tribunal to be established.

"We're creeping very close to the 60 ratifications needed," U.N. spokesman Fred Eckhard told reporters.

Bill Pace, head of Coalition for the International Criminal Court, an advocacy group, expects all 60 ratifications to be completed by mid-April, the next preparatory commission meetings for the court.

Countries are now jockeying to see who will become the 60th nation. Among those said to be preparing to hand in ratification papers are Bulgaria, Romania, Cambodia, Bolivia and Greece, diplomats said.

The court would try those accused of mass murders, war crimes and other gross human rights violations and is expected to be set up in The Hague, Netherlands, in 2003. But no one can be prosecuted for crimes committed before that time.

The U.N. Security Council has established two ad hoc courts: for war crimes during the 1990s Balkan wars and for the 1994 genocide in Rwanda. But the International Criminal Court would be the first permanent criminal tribunal, modeled after the Nazi trials at the end of World War II.

European nations and Canada have taken the lead in supporting the court. All European Union members, except for Greece and Ireland, have ratified the court statutes, negotiated in Rome in 1998. Latin American and African nations were also in the forefront in approving the court.

But Asian countries have been slow to ratify, with legal experts saying no one government wants to take the lead in approving what many perceive to be a Western-oriented tribunal that could undermine their sovereignty.

The United States is worried about frivolous law suits from developing countries against U.S. servicemen stationed around the world. The Bush administration has even asked the United Nations whether it could rescind Washington's signature from the treaty, signed by former U.S. President Bill Clinton at the end of his term.

In Congress, opposition to the International Criminal Court is led chiefly by Republicans in both houses, who have sponsored numerous amendments to bills that would cut funding for U.S. involvement in the court and end military aid to some countries that have ratified its establishment. Other proposals would authorize the use of force to free an American from the court, dubbed by Europeans as the "The Hague invasion clause."

Sponsors of the measures intend to come to some agreement on the proposals with the Bush administration by mid-April.

Last October, Belgium Foreign Minister Louis Michel, acting on behalf of the European Union, and German Foreign Minister Joschka Fischer wrote to Secretary of State Colin Powell expressing concern about the proposed legislation and asking the administration to soften it.

The 56 nations who have ratified the court are: Andorra, Antigua and Barbuda, Argentina, Austria, Belgium, Belize, Benin, Botswana, Britain, Canada, Central African Republic, Costa Rica, Croatia, Cyprus, Denmark, Dominica, Ecuador, Estonia, Fiji, Finland, France, Gabon, Germany and Ghana.

Also Hungary, Iceland, Italy, Lesotho, Liechtenstein, Luxembourg, Macedonia, Mali, Marshall Islands, Mauritius, Nauru, Netherlands, New Zealand, Nigeria, Norway, Panama, Paraguay, Peru, Poland, Portugal, San Marino, Senegal, Sierra Leone, Slovenia, South Africa, Spain, Sweden, Switzerland, Tajikistan, Trinidad and Tobago, Venezuela and Yugoslavia.