The Senate yesterday overwhelmingly approved a historic expansion of the North Atlantic Treaty Organization to include three former Cold War enemies: Poland, Hungary and the Czech Republic.

The vote was 80 to 19, with 45 Republicans joining 35 Democrats in providing 14 more votes than the two-thirds majority needed for ratification of NATO's first expansion into territory once dominated by the Soviet Union, which the alliance was created a half-century ago to contain.

In the strikingly bipartisan vote, only 10 Democrats and nine Republicans opposed expansion, including some of the Senate's most liberal and conservative members.

President Clinton, marking a key foreign policy victory, hailed the vote as "a major milestone on the road to an undivided, democratic and peaceful Europe" that would "reduce the chances American men and women will ever again be called to Europe's fields of battle." In a statement from the White House, Clinton added, "The message this vote sends is clear: American support for NATO is firm, our leadership for security on both sides of the Atlantic is strong, and there is a solid, bipartisan foundation for an active U.S. role in the world."

NATO brought the West a half-century of security, and "this, in fact, is the beginning of another 50 years of peace," said Sen. Joseph R. Biden Jr. (Del.), ranking Democrat on the Foreign Relations Committee and a key player in the ratification effort. "In a larger sense," he added, "we'll be righting an historical injustice forced upon the Poles, Czechs and Hungarians by Joseph Stalin."

Senators observed the solemnity of the occasion by sitting at their desks and rising from their chairs to vote, as Senate rules require for treaties, rather than following their usual practice of milling about the floor.

In moving to shield the three former foes under the NATO umbrella, the United States will be committing itself to defend them from military attack, as it would any other ally. The change is the largest increase of U.S. global commitment since the end of the Cold War.

Before the vote, the Senate easily defeated amendments aimed at delaying the three countries' admission and preventing further expansion for at least three years.

Approval came over objections from a disparate coalition that spanned the Senate's political spectrum. Senators warned that it could result in huge costs to American taxpayers, a poisoning of relations with Russia and a distortion of NATO's mission that could lead to dangerous new peacekeeping operations.

But approval was virtually assured before the debate even started: It was the result of months of laborious efforts by the administration and Senate supporters, reinforced by the powerful symbolism of NATO's inclusion of former Warsaw Pact members, pressure from ethnic constituencies and the prospect of new markets for the American defense industry at a time of shrinking U.S. demand.

The ratification campaign was a high point of bipartisan cooperation between Clinton and Republican leaders, who brushed aside partisan hostilities that have stalled, delayed or complicated other major legislation. NATO expansion was by far Congress's biggest achievement so far this year.

The Senate action also constituted a major new U.S. commitment abroad at a time when Congress, especially the less internationally minded House, has balked at new funding for the International Monetary Fund and jeopardized payment of back U.S. dues to the United Nations because of a dispute over abortion policy.

It was the second major international pact approved by the Senate in little more than a year. Last April, the Senate voted overwhelmingly to approve ratification of a treaty to ban chemical weapons.

Yesterday's vote was critical because Senate approval was essential for U.S. ratification of NATO expansion, and all 16 existing members of the alliance must give their approval before new members are admitted.

NATO has been expanded only three times since it was created in 1949, most recently in 1982 when Spain was admitted. Four other NATO members -- Canada, Denmark, Norway and Germany -- already have approved the expansion, as has the Czech legislature. The three new members will be admitted next year if, as expected, the rest of the current NATO members go along.

In voting on amendments yesterday, the Senate rejected, 83 to 17, a proposal by Sen. Daniel Patrick Moynihan (D-N.Y.) to delay admission of Poland, Hungary and the Czech Republic until they join the European Union. Voting 59 to 41, it defeated a proposal by Sen. John W. Warner (R-Va.) to impose a three-year moratorium on further NATO expansion. Also defeated were proposals to require congressional votes on keeping U.S. troops in Bosnia.

After intense lobbying by the administration, the Senate soundly defeated, 82 to 18, a move by Sen. John D. Ashcroft (R-Mo.) to bar NATO from peacekeeping and other activities outside members' borders.

But negotiations produced agreement on a compromise on cost-cutting from Appropriations Committee Chairman Ted Stevens (R-Alaska) to ensure Congress has at least some control over spending to assimilate the three countries.

The Senate debate -- at times impassioned, more often constrained by a sense that the outcome was preordained in favor of approval -- stretched over several days in April and most of the past four days.

The central issue was whether expansion would enhance or impede prospects for security, unity and peace among Western nations now that the old Cold War divisions are gone but Russia continues to struggle with the burdens of its past.

NATO enlargement "will make Europe more stable and America more secure," ensuring that "the new democracies of Central and Eastern Europe will share the burden of European security," said Sen. Barbara A. Mikulski (D-Md.), speaking passionately of her Polish heritage and pride in Poland's transformation.

"If NATO doesn't enlarge, the Iron Curtain remains permanent and the unnatural division of Europe will live on longer than the Soviet Empire did," Mikulski said. "NATO would remain, as {Czech President} Vaclav Havel has said, an alumni club for Cold War victories."

Arguing the reverse, critics contended it could wind up stretching NATO to the breaking point, especially if its mission is expanded as members grow, pushing the alliance into peacekeeping, resolution of ethnic hostilities and nation-building among nonmembers. "We are literally trying to create . . . a 911 organization:' Call if there is a problem, dial-a-cop, dial-a-soldier,' " said Warner.

No alliance has better served the United States for so long as NATO, Warner argued. "If it works {and} works well, why try to fix it?" he asked.

With rich irony stemming out of dramatic upheavals of the past decade, the debate also focused on the likely impact on Russia -- less from any lingering sense of the hostility that gave rise to NATO's formation than from a concern about the fragile nature of Russia's new quest for democracy and peaceful relations with its neighbors.

Some, like Moynihan, contended that NATO expansion into the former Soviet bloc would exacerbate tensions with a weakened but still nuclear-armed Russia and risk a revival of Cold War tensions. "Back to the hair trigger," he warned. Others, such as Sen. Robert C. Smith (R-N.H.), also argued it would stoke the fires of anti-Western nationalism and undermine democratic forces in Russia. The best way to ensure freedom of Eastern Europe is to ensure "a Western Russia . . . a democratic Russia . . . anything we do in any way to hinder that is a serious mistake," Smith said.

To the contrary, argued Senate Foreign Relations Committee Chairman Jesse Helms (R-N.C.), NATO's expansion will cut off any new moves by Russia to restore its western empire. "If anything, it will make it easier for us to maintain friendly relations with Russia because an expanded NATO will shut off Russia's avenues to more destructive patterns of behavior," he said.

A third major argument centered on costs of assimilating the three countries into the alliance. While the administration estimated costs to the United States at about $400 million over the next decade, opponents said the price tag could skyrocket to billions of dollars over the same period, including subsidies and other forms of bilateral assistance. CAPTION: What the Expansion Means SECURITY By voting to expand NATO to include the Czech Republic, Poland and Hungary, the Senate is endorsing the promise to treat an attack on any of those countries as an attack against the United States, in accordance with the principles governing all of NATO's 16 current members. Although new members must be prepared to host forces from other member states, the State Department does not anticipate that the expansion will require more U.S. forces in Europe. COST A NATO study cited by the State Department projects the enlargement to increase the organization's general budget by $1.5 billion over 12 years -- with $400 million of that cost borne by the United States. The general budget covers costs such as expanding air defense, conducting English-language training and updating computers. Many functions, such as coordinating command and control, conducting joint exercises and modernizing a country's own forces, are not included in the NATO budget. Those factors could push the total annual cost to $1 billion a year for the new members and $200 million for the United States, according to a Rand Corp. estimate. TIMETABLE Each member state must ratify the invitation. Four -- Canada, Denmark, Norway and Germany -- have done so, and Iceland is currently deliberating. NATO has set an informal timetable that all countries ratify the expansion by the end of 1998 so that the three countries can formally join on April 4, 1999, the organization's 50th anniversary. Votes Against NATO Growth

Following are the nine Republican and 10 Democratic senators who voted last night against admitting Poland, Hungary and the Czech Republic to NATO. Sen. Jon Kyl (R-Ariz.) did not vote. REPUBLICANS Ashcroft, Mo.; Craig, Idaho; Hutchinson, Ark.; Inhofe, Okla.; Jeffords, Vt.; Kempthorne, Idaho; Smith, N.H.; Specter, Pa.; Warner, Va. DEMOCRATS Bryan, Nev.; Bumpers, Ark.; Conrad, N.D.; Dorgan, N.D.; Harkin, Iowa; Leahy, Vt.; Moynihan, N.Y.; Reid, Nev.; Wellstone, Minn.; Wyden, Ore.