The United States and the Soviet Union appear ready to participate in a new 35-nation conference to negotiate ways to reduce the likelihood of surprise attack in Europe by monitoring movement of NATO and Soviet bloc forces there.

One goal of such a conference would be to open for the first time all of Europe, including European territory of the Soviet Union, to mandatory inspection of certain military exercises and maneuvers by either side.

Establishing such a conference to negotiate so-called confidence-building measures applicable from the Atlantic Ocean to the Ural Mountains in the Soviet Union has long been a goal of America's allies, particularly France, which originally proposed it in 1978.

U.S. officials cautioned, however, that final agreement to hold the conference is contingent on successful negotiations at the current 35-nation conference in Madrid reviewing adherence to the Helsinki accords on human rights. They said the final decision may hinge on Soviet performance on such things as Jewish emigration and Soviet treatment of dissidents.

Some initial provisions for military confidence-building measures were included in the 1975 agreement on European security, cooperation and human rights signed in Helsinki by 33 European nations, including the Soviet Union, plus the United States and Canada.

But these only required notification three weeks before exercises involving more than 25,000 troops, and covered an area only 150 miles beyond the Soviet Union's European border. It also was left to individual countries to decide whether they would invite observers from other countries to watch.

Extending that zone to the Urals 1,200 miles inside the Soviet Union would cover an area in which are based virtually all Soviet forces that could be used to attack western Europe.

U.S. officials at the conference in Madrid, which has been under way since November, 1980, said there have been signs for the past year that the Soviets would agree in principle to a new conference, but differences remained about what would be discussed.

A March 15 proposal by a group of neutral and non-aligned nations to break a long deadlock between the western and eastern blocs at Madrid over adherence to the Helsinki human rights agreement also included four key points about a future conference on new confidence-building measures. The Soviets suddenly accepted this position paper on May 6.

While western nations are still unhappy that human rights sections in the position paper are not demanding enough on Soviet behavior, they are pleased about the potential for new negotiations to avoid surprise attack in Europe.

The chief U.S. delegate at Madrid, Ambassador Max Kampelman, said in a telephone interview yesterday that "The Soviets have made a move which is encouraging in indicating a will to sit down to discuss this serious subject of surprise attack."

But Kampelman added that agreeing to a new conference still would leave tough negotiations before agreement on specific confidence-building measures.

The first indication here of what Moscow "seems to be accepting" came in a speech Tuesday night by Sen. Orrin G. Hatch (R-Utah). Hatch said "the measures must be politically binding, militarily significant, verifiable and stretch all the way to the Urals."

Kampelman, who discussed the concept with President Reagan at the White House three weeks ago, said this is consistent with U.S. ideas and the neutral and non-aligned nations' proposal.

Hatch emphasized that these criteria mean mandatory verification by inspection teams, and suggested that it could lead to advance notification of Soviet troop movements outside their garrison areas.

Michael P. Pillsbury, foreign policy adviser to the conservative Republican steering group of which Hatch is vice president, said such measures could provide the basis for a NATO-wide military alert in the face of potentially dangerous Soviet activities.

If Moscow did not allow inspection of worrisome troop movements after agreeing to such provisions in a new conference, it would make the danger clearer to the West and an alert more possible politically.

A long-standing question in NATO is whether the 15 member governments would react in time to ambiguous signs in the East. Richard K. Betts, a Brookings Institution expert, wrote in a recent book on surprise attack that, while the alliance has had partial alerts for training purposes, "NATO forces have never gone on full alert."

Some skeptical western military officials have questioned whether such measures could inhibit U.S. forces in Germany from moving out of their garrisons and closer to the eastern border in a crisis. The Soviets also have previously taken the broadest interpretation of the term "Atlantic" in the French proposal to try to gain inspection rights to the U.S. East Coast and naval maneuvers in the Atlantic.

A conference on confidence-building measures, which could begin late this year in Stockholm, would bring European countries more directly into military negotiations now dominated by the two superpowers.

It could be used by the United States and the Soviets as an indication of good faith in the struggle to influence European opinion about the forthcoming deployment of new U.S. nuclear missiles in Europe.