The agreement announced yesterday on conventional arms in Europe would place enduring limits on Soviet forces and give every country there substantial advance warning of potentially hostile military action, according to U.S. officials and independent analysts.

The accord was conceived 18 months ago as a means to lower East-West tensions and sharply reduce the likelihood of armed conflict. At the time, the military forces of the Cold War remained in place, but the promise of peace seemed great. Since then, political reforms have pulled Eastern Europe out of Moscow's orbit and set in motion the withdrawal of Soviet forces from the region, transforming the accord into a symbol of East-West accommodation.

By the standards of previous such efforts, the agreement "in principle" on major terms of the accord represents a lightning stroke. Earlier talks had lasted for 17 years before foundering from lack of agreement on the size of existing armed forces.

But many experts said the negotiators still did not move fast enough, noting that the accord allows each side to maintain far greater forces in the region than voters and legislators in each nation's capital are likely to support, barring a major turnaround in U.S.-Soviet relations.

It would keep in place roughly 20,000 tanks on each side of the Cold War line of demarcation running through a divided Germany, more than the number of tanks deployed in the region during World War II. It does not limit the current deployment of more than 305,000 U.S. troops, even though U.S. military leaders and politicians have forecast the withdrawal of up to 230,000 troops.

While it requires sharp reductions in existing Soviet arsenals, it nonetheless allows the Soviet Union to deploy more arms in Eastern Europe than Moscow's former allies are expected to tolerate. It also allows the United States to keep more aircraft, artillery and armored vehicles in the region than Germany and other U.S. allies may want.

The treaty's biggest impact will come in the establishment of a comprehensive system for monitoring major troop maneuvers and the deployment of key military equipment in the region covered by the accord, stretching from the Atlantic Ocean eastward to the Soviet Ural Mountains, many experts said.

"There will be hundreds of inspectors crawling around all of the NATO and {former} Warsaw Pact states, providing a unique early warning network for non-nuclear forces," said Lee Feinstein, executive director of the Arms Control Association. "This will be important in ways that we can't even predict."

Defense Secretary Richard B. Cheney underscored this point last month by saying that the accord would allow the United States to change significantly "our planning assumptions for the kind of forces we will require, the kinds of deployments we think are appropriate and the overall size of our military establishment." He said the inspections, plus deep Soviet arms cuts, would provide "years of warning time . . . to reconstitute the kind of military force we've deployed for the last 45 years."

Some officials believe the stage was set for a successful negotiating outcome in March 1989, when Soviet Foreign Minister Eduard Shevardnadze accepted the Western concept of reductions to equal force levels on both sides. Although this committed the Soviets to making virtually all of the force cuts under the new accord, Shevardnadze explained recently that the Soviet leadership had decided Moscow overbuilt its forces based on "an erroneous assessment" of the Western military threat "and a desire to protect the country against any eventuality."

President Bush pushed the negotiations ahead with a surprise decision two months later to accept a Soviet demand for treaty limits on aircraft and helicopters, instead of just tanks, artillery and armored vehicles. The two sides subsequently spent months working out an arrangement to limit U.S. and Soviet troops but dropped it after the dissolution of the Warsaw Pact alliance and the projected ouster within two years of all Soviet forces from the territories of its former allies.

In the end, these political developments forced the negotiations to slow, as Soviet military officials resisted concessions they felt would further weaken Moscow's drastically reduced standing in Europe. But Shevardnadze indicated yesterday that he was able to wrest new compromises that allowed an agreement "in principle."