President Clinton announced yesterday that United States will not join an international treaty banning antipersonnel land mines, resisting worldwide pressure on grounds the ban could put U.S. troops at risk in time of war, which he called "a line I simply could not cross."

The U.S. withdrawal from negotiations, which came the same day that 89 countries meeting in Oslo, Norway, endorsed the treaty language, was greeted with jubilation and relief by humanitarian groups and countries that support the ban. Many negotiators believed Washington was trying to dilute the treaty with a last-minute counterproposal and a flurry of telephone calls between the White House and foreign heads of states.

"We are not prepared to pay any price" for Washington's approval, said Canadian Foreign Minister Lloyd Axworthy, who spearheaded the process.

The treaty prohibits countries from using all antipersonnel land mines, small explosive devices that have created a humanitarian crisis because they maim and kill 25,000 civilians each year, many in countries no longer at war. Signatories will have up to four years to destroy their stockpiles of land mines, and up to 10 years to clear areas that have been mined.

The Pentagon praised Clinton's decision and Senate Foreign Relations Committee Chairman Jesse Helms (R-N.C.) called it "a courageous act." But Sen. Patrick J. Leahy (D-Vt.), the foremost U.S. advocate of a ban, pledged to push ahead with legislation to ban land mines that has already won bipartisan support.

At a news conference with his top national security advisers, Clinton said he believed the United States had gone "the extra miles and beyond" to seek a compromise on the treaty. But some administration officials acknowledged the United States had gotten into the negotiations too late to shape a treaty that could be accepted by the Joint Chiefs of Staff.

Instead, the administration was put on the defensive from the moment its negotiators arrived in Oslo a month ago and were seen as a agents of a superpower trying to manipulate a 13-month-long, grass-roots campaign that had grown into a worldwide humanitarian crusade.

"I'm pleased the United States had the grace to withdraw. . . . I'm proud of the governments who stood up to the onslaught of the remaining superpower, coming in and pushing and shoving to get its way," said Jody Williams, head of the International Campaign to Ban Landmines. "We hope President Clinton will take his confused internal policy home and fix it. But that is not our problem."

However, many proponents of the treaty have argued that U.S. participation is essential to the success of the ban. Without U.S. leadership, they believe it will be more difficult to persuade the world's largest users and manufacturers of land mines, including China and Russia, to join the treaty. Neither country participated in the Oslo negotiations.

Seeking to deflect criticism, Clinton also announced a series of unilateral initiatives, including a request to Congress to add $12 million to U.S. efforts to help other countries clearing their lands.

However, the measures would not, as Clinton said yesterday, "eliminate all antipersonnel land mines from America's arsenal."

Clinton's top arms control adviser, Robert Bell, told reporters after the news conference that the United States had no intention of finding alternatives to the millions of antipersonnel land mines it uses to prevent enemy troops from breaching antitank minefields. The vast majority of the antipersonnel land mines the United States now uses are for that purpose.

Pentagon officials who reviewed an advance copy of Clinton's text tried unsuccessfully to get the White House to remove the inaccuracy. Later in the day, Defense Secretary William S. Cohen issued a statement saying, in part, that U.S. troops "will continue to deploy" antipersonnel mines used to protect antitank mine fields.

Some of Clinton's other measures fell short of the U.S. counterproposal at Oslo. Yesterday, he said that he had directed the Pentagon to find alternatives to other self-destructing mines, or "smart mines," by 2003. In its counterproposal late last week, the Clinton administration agreed to give up use of those mines.

Clinton also directed the Defense Department to find alternatives by the year 2006 for the antipersonnel mines the United States stockpiles for use in Korea, the same amount of time offered in the counterproposal. He also pledged to redouble U.S. efforts to win a global antipersonnel land mine ban in the United Nations Conference on Disarmament in Geneva, which this year failed to begin talks requested by the United States on land mines.

The ban approved in Oslo is supported by many U.S. allies, including Britain, Germany and Mexico, but is opposed by many states that produce and use mines, including China, Russia, India, Pakistan, Iran and Iraq. South Korea, Kuwait, Japan and Israel also oppose it.

Humanitarian organizations that lobbied for the unprecedented disarmament treaty, the first arms control treaty to limit a conventional weapon, were jubilant at the outcome of the grueling negotiating process, initially dismissed as quixotic and unrealistic.

Support for the treaty gathered momentum this year from the well-publicized sponsorship of Diana, Princess of Wales, before her death the day before the conference opened.

"Humanity still has the power to move nations," declared Louise Doswald-Beck of the International Committee of the Red Cross, one of the leaders of the land mine-ban campaign. "This is a wonderful day for international humanitarian law."

Jan Egeland, deputy Norwegian foreign minister, predicted Clinton will support the treaty by December. "I believe internal forces in the United States will be tremendous," he said.

Representatives of the Canadian government, which initiated what has become known as the "Ottawa process" to seek a ban, popped champagne corks and smiled for photographers in the halls of the conference center in Oslo.

The text is set to be adopted without a vote today, with a formal ceremony following Friday. On Dec. 3, the process will move to Ottawa, where as many as 100 countries will sign the treaty. Ratification by individual member states will then ensue, and the treaty will enter into force when 40 nations have ratified it, probably within two years.

Antitank mines, which are set off by the weight of a large vehicle or by the magnetic force of large metal objects, are permitted under the ban, as are many kinds of anti-tampering devices, booby traps used to stop enemy troops from removing them.

Treaty proponents refused to exempt the U.S. method for protecting antitank mines, which is to scatter antipersonnel mines among them. Proponents believed an exemption on this use of antipersonnel mines would give other nations a way to get around the ban.

The United States also had asked for a special waiver for Korea, where 1 million South Korean non-self destructing mines are laid and the United States maintains another 1 million so-called dumb mines for use there. Some 37,000 U.S. troops are stationed there and face an army of 1 million North Koreans.

A treaty provision designed for the poorest nations where mines laid in wartime remain major killers -- Angola, Afghanistan and Cambodia are the most commonly mentioned ones -- allows an extension of the 10-year period granted other countries to accommodate the huge financial expense of removing them. The international ban campaign estimates the cost at $300 per mine, and the number of extant mines at 10 million. Priest reported from Washington, Trueheart from Oslo. CAPTION: Clinton gestures, with Defense Secretary Cohen and adviser Samuel R. Berger.