King Hussein, who served as the compliant salesman of America's Middle East policies in the Arab world for decades, has recast himself in the startling new role of spokesman for the Arab states opposed to the U.S.-sponsored Camp David peace accords.

Expecting to visit Washington sometime this spring or early summer, the king has been given an informal mandate by his Arab allies, most notably Iraq and Saudi Arabia, to try to convince the Reagan administration of the wisdom of abandoning the Camp David process and starting new negotiations to include the Palestine Liberation Organization.

For an Arab leader who was once widely regarded as a ward of the United States, the transformation in his role and image both here in the Arab world and abroad seems truly extraodinary.

Hussein was for years politically and financially dependent on the United States for his survival and served as a conduit for American views on the issues of a war and peace in the Middle East with other more radical Arab governments. On several occasions, Washington acted directly or through Israel to ensure the survival of his throne, seriously threatened in 1970 by PLO guerrillas with whom he fought a bitter battle during what is known as Black September.

Thus, there is more than one irony in his staunch opposition to current American Middle East Policy today and his championing of the Palestinian cause on behalf of both the PLO and other Arab capitals outside Cairo.

But times have changed and with them the main financial and political, if still not military, backer of the Hashemite kingdom on the east bank of the Jordan. Since the 1978 Baghdad Conference of Arab leaders opposed to the Camp David accords, Jordan has been receiving an estimated $1 billion annualy in Arab financial aid, primarily from Saudi Arabia and Iraq, its two closest present-day allies.

This helps to explain among other things, Hussein's strong support for Iraq in its ongoing war with Iran despite warnings from Washington early on in the fighting that this could become a political liability. So far, however, he has been richly rewarded for this backing by Iraq, which has passed on 30 to 40 American-made M60 tanks captured from Iran and agreed to settle a longstanding border demarcation feud in Jordan's favor.

At the last Arab summit held in Amman last November, the king was given an informal mandate from both Iraq and Saudi Arabia to present to President Reagan what is portrayed here as the concesnsus of Arab opinion outside Cairo toward the stalled Palestine autonomy talks. As the Arab leader with the longest and closest ties with various American administrations. Hussein seems ideally suited for this role as spokesman.

But his mission even in an initial phase of exploratory talks is being directly challenged by Syria, which has come to regard itself as the main champion of the Palestinian cause in the Arab world, particularly in the wake of the Camp David accords.

Syria refused to attend the Amman Arab summit and convinced the PLO as well as three other Arab states to boycott it, too, under considerable pressure. But PLO chief Yasser Arafat subsequently met with Hussein during the Islamic conference in Taif, Saudi Arabia, late last month.

Because of Syria's growing hostility toward Jordan -- highlighted by a reported Syrian-instigated attempt on the Jordanian prime minister's life early this month -- King Hussein will have to tred a careful path in his talks with the Reagan administration to avoid doing anything to suggest a separate Jordanian peace with Israel may be possible.

Both the American and Israeli notions of what is being called the "Jordanian option" have tended to veer in this direction under the guise sometimes of including Jordan now in the Camp David talks. But Egyptian President Anwar Sadat has also rejected Jordanian participation in these talks at this time, effectively leaving the option without an Arab sponsor and complicating further the next move in American diplomacy to break the current impasse in the Middle East peace negotiations.

Hussein has yet to detail his own views on the deadlocked Camp David negotiations. But he has condemned them as a "dead horse," emphatically rejected prevailing American and Jorandanian notions of the Jordanian option, said the PLO is the only representative of the Palestinian people and publicly urged Washington to accept this "reality."

He has also said that the initial step must be to "define first of all what the elements of peace must be in a clear and acceptable way."

Western diplomats and Jordanian sources here do not at this point expect the king to present President Reagan with any concrete Jordanian or Arab proposals but rather to try to persuade him to break with the Camp David approach and reconsider some of the fundamental issues involved in the stalled Palestine autonomy talks before he formulates a new American Middle East policy.

Discussing in some detail the Jordanian view of the so-called Jordanian option, Crown Prince Hasan Ibn Talal in an interview called for a period of "substantive ground turning" to clarify the obstacles now blocking the Camp David negotiations.

"I think what has to be negotiated is a very wide scope of issues," he said, dismissing the contention of former U.S. Middle East peace negotiator Sol Linowitz that only 5 percent of the issues were left to be resolved.

"Where do we stand on the holy places? Where do we stand on sovereignty [for the Palestinians]? Where do we stand on borders?" he asked by way of citing some of the issues he and, presumably, his brother King Hussein feel must be reopened for negotiation.

The views of the concern prince, who has made West Bank economic and political issues his specialty, are believed by Western Analysts here to reflect fairly closely the feelings of King Hussein as well.

He said Israel had to disengage itself from its "very rigid, ideological, Biblical stand" toward the West Bank and its opposition to the idea of a Palestinian "entity" being established there.

Asked about the kingdom's current attitude toward Hussein's proposal in the early 1970s for a federation between Jordan and an autonomous Palestinian entity in the West Bank and Gaza Strip, Hasan did not rule it out as a possible solution. But he said the decision on a federation or a separate independent state would have to be left open for the Palestinians themselves to decide. CAPTION: Illustration, Jordan's King Hussein, who get about $1 billion a year in Arab financial aid. By Steve Mendelson for the Washington Post