President Carter temporarily scrapped the strategic arms limitation treaty (SALT II) with the Soviet Union yesterday as the administration readied other proposed measures, including renewed military and economic aid to Pakistan, in response to the Soviet invasion of Afghanistan.

In a letter to Senate Majority Leader Robert C. Byrd (D-W.Va.), Carter reaffirmed his support for SALT II, but asked the Senate to postpone indefinitely its debate on the treaty because of the crisis in Afghanistan.

With the treaty doomed to almost certain defeat because of last week's Soviet invasion, SALT supporter Byrd quickly agreed to the White House request.

"It would not be conducive to the SALT process to bring up the treaty at this time," Byrd said. "The treaty can stay on the Senate calendar and be brought up at a future date, depending on events."

Both Byrd and White House officials insisted that the postponement of the Senate debate, which had been scheduled for next month, did not mean that the proposed treaty is a dead issue. But the decision to put off the debate cheered treaty opponents, who predicted that it will languish at least through this year and may never be resurrected.

White House press secretary Jody Powell announced the president's SALT decision as administration officials continued to consult with congressional leaders and U.S. allies on a broad range of measures Carter has tentatively approved in response to the Afghanistan invasion.

Some of these measures, sources said, include the resumption of U.S. aid to Pakistan, which borders Afghanistan, and a ban on sales of high-technology items such as computers to the Soviet Union.The sources also did not rule out the possibility of other restrictions on sales to the Soviets, including sales of grain.

Powell raised the possibility that the proposed substantial increase in defense spending that Carter announced last month, in part to placate SALT critics in Congress, could be even larger because of the Soviet actions. The president said he will propose $157 billion in military spending for the fiscal year that begins Oct. 1, and called for steady and sustained growth in the defense budget over the next several years.

In his letter to Byrd, Carter said he was not asking for withdrawal of the tready, which he said remains "in the national security interest of the United States and the entire world," but urged deferral of the debate so that he and Congress can "devote our primary attention to the legislative and other measures required to respond to this crisis."

Those legislative measures were not detailed, but officials privately confirmed that they will include an effort to clear the way for resumption of U.S. economic and military aid to Pakistan. This was terminated last April because of Washington's belief that Pakistan is secretly building an atomic weapons capability.

Chairman Clement J. Zablocki (D-Wis.) of the House Foreign Affairs Committee and Rep. Jonathan B Bingham (D-N.Y.), chairman of the subcommittee handling nuclear weapons proliferation, announced they will sponsor a special authorization for the Pakistani aid, in effect overriding the provisions of the non-proliferation laws that required the aid cutoff.

Zablocki said he and Bingham remain committed to preventing the spread of nuclear weapons, but said the threat to Pakistan poses an extraordinary situation that requires an exception to U.S. laws. Pakistan is reported to be continuing its work on an atomic weapons capability, but technical difficulties are said to be slowing this effort.

Chairman Frank Church (D-Idaho) of the Senate Foreign Relations Committee is reported to have approved an aid-to-Pakistan measure for Senate consideration.

Meanwhile, administration officials said the United States has sent messages in the past few days asking major allies in Western Europe and Japan to cooperate in a joint effort to tighten technological sales to Moscow. As of last night, the sources said the degree of cooperation the admdinistration can count on was not clear.

Past attempts to impede the Soviets' ability to buy such items have been frustrated by the willingness of other countries to provide products denied by the United States. For example, when the United States blocked the sale of a computer to the Soviet news agency, Tass, Moscow simply bought one from France.

Among the unilateral steps being-weighed by the administration, the sources continued, is a forced reduction of the number of diplomatic and consular personnel the Soviets are allowed to keep in the United States. The number of Soviet journalists stationed in this country also could be cut.

The sources said this reduced level of diplomatic representation also could mean a U.S. decision to postpone indefinitely the planned openings of a U.S. consulate in Kiev and of a new consulate the Soviets were to get in New York in exchange.

Also under consideration, the sources said, is a possible attempt to change U.S. maritime regulations to place much more stringent restrictions on the ability of Soviet ships to call at U.S. ports and use their services.

The nuclear-powered Nimitz, largest carrier in the U.S. fleet, left Naples, Italy, yesterday en route to the Arabian Sea off Iran to replace the Kitty Hawk, Navy sources told United Press International.

The 95,000-ton Nimitz must sail around Africa because it is too large to negotiate the Suez Canal. It is due to arrive off Iran at the end of January.

Carter last month ordered the Nimitz to duty off Iran.

The Pentagon told UPI 20 U.S. ships are in waters off Iran and the Middle East. Sources said the Soviet Union has dispatched 23 ships to the area -- about half warships, the rest support vessels.

Postponing the SALT debate and planning to renew Pakistan aid illustrated how the invasion of Afghanistan has overwhelmed Carter's most cherished foreign policy goal -- control and eventual reduction of the world's nuclear arsenals.

A senior White House official called the SALT decision "regrettable," and said it was forced on the United States by the Soviet Union's "illegal invasion" of a neighboring country. He said the United States would continue to abide by the limits set in SALT I, but said the "onus" for delaying the more recent accord rests on the Soviets.

The president's decision was applauded by SALT opponents, who contended that the treaty was in grave danger of defeat in the Senate even before the Afghanistan or Iran crisis.

"They knew they didn't have enough votes to ratify the agreement [last month], and they have even less votes now," said Sen. Henry M. Jackson (D-Wash.).

Senate Minority Leader Howard H. Baker Jr. of Tennessee and former California governor Ronald Reagan, both GOP presidential hopefuls, said the considered the SALT postponement a victory for them and other treaty opponents.

The strongest statement came from another Republican contender, former Texas governor John B. Connally, who said the United States should be "out trying to mobilize the whole world against the Soviet Union" and should set a deadline for release of the American hostages in Iran.

In Waterloo, Iowa, last night, Vice President Mondale called the Soviet action in Afghanistan an "absolutely indefensible, maked invasion of an independent country." Mondale said the Soviet backed coup "goes to the basis of a civilized world, a peaceful world and the principle of detente."