President Reagan yesterday called for the destruction of all U.S. and Soviet intermediate-range nuclear missiles "by the end of this decade." At the same time, however, he said Soviet leader Mikhail Gorbachev's proposal to eliminate all nuclear weapons by the end of this century is "clearly not appropriate for consideration at this time."

Instead, Reagan linked "the total elimination of nuclear weapons" to a series of long-term goals including the reduction of Soviet conventional forces to bring them into balance with the West, "full compliance" by the Soviets with existing arms treaties, "peaceful resolution of regional conflicts," and "a demonstrated commitment by the Soviet Union to peaceful competition."

Reagan's statement, which aides said summed up a private letter sent to Gorbachev over the weekend, was an answer to the Soviet leader's Jan. 15 proposals in a wide variety of arms control areas. Foremost among them was Gorbachev's widely publicized plan to eliminate all nuclear weapons by the year 2000.

Sources said the Reagan letter did not provide any new U.S. positions in other negotiations outside intermediate-range nuclear forces (INF). Instead, the president made the point that other steps have to be made "in parallel" to pave the way the "ultimate goal" of nuclear disarmament.

While delaying complete nuclear disarmament indefinitely, Reagan said he hoped for "immediate progress" in the Geneva INF talks, according to a statement released by the White House. U.S. negotiators, Reagan added, began yesterday to present "a concrete plan" to eliminate all U.S. Pershing II and ground-based cruise missile and Soviet SS20 missiles within three years beginning in 1987. Gorbachev also had focused on INF but proposed that only the European-based missile systems be destroyed in the next five to eight years. He made no specific proposals about reducing Soviet SS20 systems based in Asia and the Far East, an omission which worries U.S. allies in the region.

The Soviet Union has 441 SS20 missiles overall, according to U.S. intelligence sources. About 270 are considered based in the European portion of the Soviet Union, with the remainder in the Asian and Far Eastern portions of the country. The United States has so far deployed about 168 of the 224 intermediate-range missiles it planned to base in Western Europe. All 108 Pershing missiles are operational in West Germany; 60 of the planned 116 ground-launched cruise missile launchers are currently based in England, Italy, Belgium and West Germany.

Under the U.S. proposal presented in Geneva yesterday, a complex formula would control the elimination of the two sides' intermediate-range missiles over the three-year period. After the first year, both sides would be permitted only 140 launchers in Europe. The Soviets, which would be cutting their European forces by about 50 percent, would have to make the same size cut in their Asian and Far Eastern forces.

Thus the Soviet force of 441 would be reduced by roughly 220 launchers while the U.S. cut would be only about 28. While the Soviets would be required to destroy their systems, the U.S. missiles could be returned to the United States to balance off the 90 SS20s the Soviets still had in the Far East. In the second year, both sides' European forces would drop to 70, while the Soviet Far East force would be trimmed to about 44. At this point, the United States also would begin destroying its systems since it would only be allowed 44 based in the United States.

In the final year, both sides would eliminate their remaining intermediate-range missiles.