A Mideast monarch who speaks softly and pilots his own jets

This is Hussein speaking,'' says the oddly un-kinglike voice on the telephone line. The tone hints at the complex mix of influences, experiences, and character traits that have helped Hussein ibn-Talal - thrust onto the throne as a teen-ager back from school in Britain in the 1950s - steer Jordan through 32 years of Middle East strife in a world where working monarchies are supposed to be the stuff of historical footnotes.

A daunting mix of old and new challenges now faces the King.

Grandson of the Saudi-born leader whom London installed in newly created Jordan after World War I, Hussein rules a nation whose population is mostly Palestinian. That has always been challenge No. 1 for the Jordanian monarchy - boiling into a civil war with the Palestine Liberation Organization (PLO) in what the Palestinians dubbed ''Black September'' 1970. But the demographic balance has taken on new significance with waning prospects for the Palestinians' negotiated return to areas now controlled by Israel.

Also, Hussein and other relative moderates in the Arab world must now reckon with the recent upswing of extremism, particularly Iran-style Shiite Muslim militancy, in the region.

This threat is a more amorphous one - and may be of greater immediate relevance to other Arab states than to Jordan, with its almost totally Sunni Muslim population. Yet the general concern, shared by Hussein, is that this and other brands of extremism, further encouraged by grass-roots despair over prospects for a negotiated Arab-Israeli settlement, could finally ''disintegrate'' the current Arab power lineup.

The man who will chart Jordan's course has changed, learned, and survived much in three decades on the throne. He has lived through his share of danger - beyond the several attempts on his own life.

As a boy accompanying his grandfather, King Abdullah, to the Al Aqsa mosque in the then-Arab half of Jerusalem in 1951, Hussein saw a Palestinian extremist gun down the monarch. One bullet glanced off a medal on the young Hussein's chest. In 1967, Hussein's impulse to seek Arab unity prodded him to join Egypt in a quick and disastrous war with Israel - forfeiting the Palestinian West Bank of the Jordan River 17 years after Abdullah had formally annexed it.

In the 1973 war, Hussein chose caution, deciding against joining the more successful, surprise assault on the Israelis by Egypt and Syria.

But in some respects, Hussein displays a constancy of character and credo that has proved essential to survival in those turbulent years. He remains, fundamentally, a cautious man - a leader who seeks regional consensus, safety in numbers.

''Hussein,'' says a diplomat who has dealt closely with the King, ''is no Anwar Sadat. He is not going to embark on a go-it-alone peace with the Israelis.''

Indeed, when Mr. Sadat, Jimmy Carter, and Menachem Begin brashly wrote a Jordanian role into the 1978 Camp David accords, the King took an indignantly out-front role in Arab rejection of the pact. In a palace news conference at the time, Hussein seemed as much personally wounded by Sadat's high-handedness as by the political implications of Camp David.

Fundamentally pro-Western - and with a keen understanding of the West unsurprising in a graduate from Britain's prestigious Harrow School and Sandhurst Royal Military Academy - King Hussein is also profoundly Arab and Jordanian. His public addresses are delivered in a resonant, literary Arabic - without the flamboyant colloquialisms and rhetoric of a Yasser Arafat or Sadat.

When Camp David came along, Hussein's distinctly Western inclination to opt for a negotiated resolution of the Arab-Israeli conflict paled before his Arab, and Jordanian, sense that a separate peace would both split the Arab world and encourage Israel to drive an unacceptably tough bargain.

It was the Arab in Hussein, too, that rejected private American entreaties to view Camp David as a negotiating ''process'' that would erode Israel's hold on the West Bank. ''Show me what is at the end of this 'process.' Give me guarantees,'' the King told the Americans.

And it is the Jordanian in Hussein that prompted him in 1970 to order his largely Bedouin Army - small, but reputedly the best trained in the Arab world - to drive out Palestinian guerrillas who had come very close to installing a rival government. His caution explains his reluctance to make that move until his throne was visibly at stake.

Similarly, after waiting unsuccessfully for some time for the United States to remove Israeli-requested restrictions on missile sales to Jordan, the King turned to Moscow in the early 1980s for a small batch of Soviet arms.

But Hussein is, above all, a proud and private - and oddly shy - man who has managed to transmit his own identity and values to a nation artifically created by Britain and buffeted ever since by Mideast turmoil. Among Jordan's indigenous population, including many once-nomadic Bedouin, the King is viewed with something approaching awe. Economically, Jordan, poor in resources, has impossibly prospered. Politically, Jordan, despite its Palestinian majority, has survived and, since the 1970 war, achieved stability.

It is a tribute to Hussein's rule that a good chunk of his Palestinian subjects seems genuinely to admire and support the King - and that even detractors often speak of him with a respect few other Mideast leaders enjoy.

''He has integrity - he does not listen to rumors or denunciations, preferring to check such tales with the source. And he works nonstop,'' says a Jordanian who has worked with the King. ''These traits have helped ensure stability.''

Another pillar of stability, an official adds, has been Jordan's large, effective intelligence service - though he maintains that since an internal reform in the 1960s, the apparatus has forsworn the tools of violence characteristic of the secret police in various other Mideast states.

But the person of King Hussein is Jordan, at a time when Jordan is at the very crux of the Arab-Israeli equation. Though he has surrounded himself with some of the sharpest advisers in the Arab world, he is said by aides often to be involved at even early stages of decisionmaking - notably ''on issues where he has always had primary interest, expertise, and concern: like foreign affairs and defense.'' The same goes for civil aviation, a priority area for a monarch who, as a trained pilot, often flies his own aircraft on foreign visits.

His grueling work schedule, say aides, is almost surely a major explanation for the stomach ailment that hospitalized him for several days earlier this month. ''He was supposed to have a ski vacation last month'' with US-born Queen Noor (the former Elizabeth Halaby), says one of the King's associates. ''In the event, he did go to Austria, but managed only a day or two of rest.''

''He virtually refuses to take time out for himself,'' the Queen adds privately, with a mix of admiration and concern.

Hussein's hospitalization, announced by the palace, promptly sparked speculation among Jordanians over his health. It was in response that the King, from his hospital bed, arranged a surprise phone call to a popular morning talk show on Amman radio.

''This is Hussein speaking,'' he began - and assured Jordanians he would soon be back on his feet.