King Hussein of Jordan has decided to turn to Moscow for new air defense missiles, an action that "could complicate" U.S.-Jordanian arms relations, the State Department said last night.

Reluctant confirmation of Hussein's decision, together with the first hint of its consequences here, came from a State Department briefing as the Jordanian monarch left Washington after meetings with President Reagan and other high officials.

The weapons deal, reportedly involving SAM6 surface-to-air missiles, would be Hussein's first with Moscow. He had hinted several times that he would turn to the Soviets if suitable U.S. arms were not forthcoming.

Complications that may result from the purchase were not spelled out by the senior State Department official who briefed reporters. However, they may include political repercussions on Capitol Hill and on U.S. public opinion, and Pentagon concern about security of U.S. military technology if Soviet technicians or advisers are part of the sale.

No confirmed information on the quantity or cost of the Soviet weaponry was available last night. The State Department official referred to the purchase as "limited to certain air defense items in the context of an essentially American-equipped military force."

There were unconfirmed reports that Libya had offered to pay for the Soviet weaponry, as well as reports that the money for the missiles might be coming from Iraq.

In his talks here, Hussein discussed possible purchase of advanced U.S. aircraft to augment his U.S. F5 interceptors. But no commitments came out of the talks, and there was little indication of progress.

Despite the difficulties over weaponry, Hussein and his hosts described this week's visit as positive overall. The State Department briefing officer expressed the view that the meetings "restored confidence and the relationship of trust that have traditionally characterized our relations" after a period of "very cool" relations during the Carter administration.

Hussein gave no sign that he might his longstanding refusal to join the Camp David peace process. The king was "frank to say" in his discussions here that in his view, "Camp David is inadequate as a framework for solving the Palestinian question," according to the State Department.

Hussein reportedly had good things to say about an eight-point program for an Arab-Israeli settlement espoused by Saudi Arabia's Crown Prince Fahd. This program was described in positive terms by Reagan and other high officials in the wake of the Senate vote permitting the sale of radar planes to Saudi Arabia. However, Israel objected strongly, and the United States has ceased saying anything substantive this week about the Fahd proposals.

U.S. officials have watched with dismay as a dispute between Israel and Western European nations over the Fahd plan and other Mideast views threatened to torpedo European participation in the planned multinational force to police the Sinai.

U.S. diplomats in Europe and the Mideast are reported to be seeking to avert a collision over what is regarded here as a semantic dispute.

The Jordanian-Soviet missile deal grew out of a long history of unhappiness on the part of Hussein about restrictions placed by the United States, at the behest of Israel, on the arms supplied by Washington to Jordan.

After first refusing to supply an air defense to Jordan following the 1973 Middle East war, the Ford adminstration agreed to sell Hawk anti-aircraft missiles, but only after pledging to Congress that the weapons would be "fixed, defensive and non-mobile."

In pursuit of this pledge, the wheels were taken off the Hawk missiles for the desert kingdom so that they could not be moved to the vicinity of the Jordanian-Israeli border. This action "still rankles" in Jordan, the State Department briefer said.

The growing military tension last fall between Jordan and Syria is believed to have generated Jordanian military pressure for new anti-aircraft weaponry, including mobile missiles such as the SAM6. Additional pressures were generated when Israeli planes flew over Jordanian territory in the bombing raid last June against Iraq's nuclear reactor.

In some accounts, the Israeli overflights were a deep humiliation to Hussein, who is a pilot himself, making it nearly certain that he would move quickly to improve his air defenses.