The leaders of Norway and the Netherlands are to meet here with President Carter this morning in an urgent effort to resolve difficulties before next week's NATO vote on deployment of new U.S. medium-range nuclear missiles in Western Europe.

Dutch Prime Minister Andreas van Agt's sudden decision to fly to Washington came yesterday shortly before the Dutch parliament, by a vote of 76 to 69, rejected the plan for production and deployment of the new weapons. The vote, while not binding, increases pressure on Van Agt's Cabinet to oppose the plan at the Dec. 12 NATO meeting in Brussels.

Before departing Oslo on his surprise trip, Norwegian Prime Minister Odvar Nordli said he sought the meeting with Carter "to emphasize the importance of having real negotiations" with the Soviet Union on reduction of missile arsenals in Europe.

Danish Foreign Minister Kjeld Olesen, whose government has urged a six-month dealy on the NATO decision, also arrived here for talks today with Secretary of State Cyrus Vance.

Both Van Agt and Nordli are said to be pressing for a public U.S. commitment to arms control talks with the Soviets to explore whether Moscow is prepared to negotiate meaningful reductions in its nuclear missiles aimed at Western Europe.

The plan for modernization of the NATO European-based nuclear force has revived the traditionally strong pacifist and neutralist tendencies in Norway, the Netherlands and Denmark. Today's flurry of high-level discussions apparently was designed, at least in part, to be seen as a last-ditch effort by the European leaders to prevent another upsurge in the arms race.

The three NATO countries all strongly favored an early passage of the Soviet-American strategic arms limitation treaty. The visits were arranged before it was announced yesterday that there will be no Senate SALT II debate this year, a move that considerably dimmed prospects that the treaty will ever be ratified.

Indeed, the Western consensus on the deployment of new U.S. nuclear weapons to offset Soviet buildup in the European theater was worked out under the assumption that SALT II would win Senate passage.

It is unclear what impact yesterday's SALT announcement would have on the forthcoming NATO meeting in Brussels.

U.S. officials expressed confidence yesterday that the Brussels meeting of NATO foreign and defense ministers will approve the plan for production of 572 Pershing II and Tomahawk cruise missiles and their deployment in 1983. Pershing's range is 1,000 miles, while cruise missiles have a range of 1,500 miles. Both would be capable of reaching targets in the Soviet Union, something land-based missiles in Western Europe currently cannot do.

The NATO decision, U.S. sources said, will be coupled with an offer of immediate talks with the Soviet Union on reducing stocks of medium-range missiles on both sides. Without a decision to build and deploy new U.S.missiles, the officials said, Moscow has no incentives to limit or reduce its 2,500-mile-range SS20 missiles.

According to intelligence estimates, about 120 SS20s are currently deployed in Western Russia, capable of hitting targets in Western Europe.

The Soviets have mounted an intensive diplomatic campaign to prevent a NATO decision on modernization of its nuclear forces in Europe.

Warsaw Pact foreign ministers yesterday appealed to NATO states to reject the missile plan. They reaffirmed an earlier offer made by Soviet President Leonid Brezhnev to open negotiations on limiting nuclear arms in the European theater.

After a two-day meeting in East Berlin, the Warsaw Pact issued a communique saying, "The acceptance of a proposal on the production and deployment of new types of American-made missiles in Western Europe and the realization of this proposal would destroy the basis for negotiations."

The wording of the communique suggested that the Soviets would be prepared to begin negotiations if NATO approves the modernization plan but before the new weapons are deployed, according to analysts here.

Norwegian sources said that their prime minister is expected to support the modernization program but that he wanted Carter's assurances that the subsequent talks with the Soviets "should be meaningful and should start as soon as possible."

The Dutch, however, while inclined to support Washington, face a difficult position at home. Van Agt's Christian Democrats, with their junior Liberal Party partner, have an overall majority of only two seats in the 150-member parliament. But many members of Van Agt's bloc are vigorously opposed to the modernization plan.

The Dutch prime minister flew to Rome and London yesterday in an effort to avert a possible Cabinet crisis by seeking allies' assurances and support. The British and the Italians support the plan. Italy's parliament approved it yesterday by a 328 to 230 vote.