"Tell me now, how goes it in Washington?" King Hassan II of Morocco once asked his ambassador to the United States, Badreddine Senoussi.

Telling the story later, Senoussi, who was Hassan's envoy here from November 1971 until October 1974, said he informed the king that things went well enough.

When Hassan asked how it went around the White House, Senoussi had to admit he did not know.

"Why not?" asked the king, shocked by such an admission.

"I have not been back there," Senoussi explained, "since the day I presented my credentials."

Few ambassadors have.

Epicenter of power though it may be, and for all the potential offered by high-level friendships over candlelit dinners, Washington as the diplomat's ultimate career assignment, nevertheless, can be a frustrating waiting game.

In fact, the most many of the 135 chiefs of mission assigned here can hope for is to meet the president of the United States once - when they present their beribboned credentials. After that, if they see anyone higher than the deputy secretary of state for anything less than war, it is probably at the infrequent diplomatic receptions secretaries of state have been known to give.

Held up this summer by President Carter's two foreign trips and subsequent seclusion at Camp David, the ambassadors of Great Britain, Cyprus, Saudi Arabia, Brazil and Venezuela waited between 12 and 76 days to pay their calls.

"Obviously," observed one embassy official dryly, "things of greater importance take precedence over things of lesser importance."

Aware of their instant access to world leaders through modern communications, recent American presidents often have shown little urgency in receiving the envoys sent by those leaders.

Richard Nixon set a five-ambassador minimum before he would schedule credentials presentation ceremonies. Jimmy Carter, who also prefers five, on occasion will book three in an afternoon.

Carter is also more generous with his time than some of his predecessors. He allots each envoy up to seven minutes for a private conversation.

Nixon held fast at five minutes and Lyndon Johnson stuck at two although he occasionally stretched it to five if he considered the country important enough.

Often criticized for his "assembly line" methods, Johnson once stunned an Asian ambassador groping for something to say after the ceremony by putting his arm around the envoy, spining him around and pointing out the door by which he would exit. "That's it, Mr. Ambassador," said Johnson.

Normally, though, the moment an ambassador can expect to converse privately with the president comes immediately after the presentation.

"If you have a special problem you can bring it up then," says a Latin American ambassador of the Oval Office meeting, "but it must be very, very important. Otherwise, the State Department handles it."

Complains another ambassador who remembers a full 15 minutes with the queen of England, "It's merely show. There's not much you can tell the president in five minutes."

(The ambassador's formal remarks actually are written in advance. He submits a copy to the secretary of state when he arrives. The president's reply is subsequently drafted and exchanged at the same time the ambassador offers his letter of credence and his predecessor's letter of recall.)

The Washington waiting game begins the moment an envoy arrives in town. As he advances in status from "ambassador designate" (the period prior to presenting copies of his credentials to the secretary to state) to "appointed ambassador" (the period that follows), he also moves closer to his White House appointment. Throughout it all he is advised to keep a low profile.

A kind of diplomatic Catch-22, the State Department handbook for a newly-arrived ambassador tells him not to call "formally upon other United States officials or members of the Diplomatic Corps until he has made his call upon the President. He may, however, host and attend national day receptions and small dinners as appointed Ambassador."

Secretary-General Alejandro Orfila of the Organization of American States, recalling his own 84-day wait as ambassador-designate of Argentina during Richard Nixon's Watergate winter of 1973-74, says though he was in "limbo" as an "ambassador designate" he started working from the first day he was in town. "Imagine spending three months doing nothing."

Orfila believes that he holds the decade's record for cooling his heels the longest although Venezuela's new ambassador, Marcial Perez Chiriboga, with a 76-day wait, is running a close second.

Sometimes presidential aides have resorted to innovation to comply with the Constitution (Article II, Section 3, states that the president "shall receive ambassadors and other public ministers"). When Woodrow Wilson was stricken by a stroke, three ambassadors were granted "provisional recognition" until he was well enough to receive them in his wheelchair.

Aides to Dwight Eisenhower, following his heart attack, decided an ambassador's "letter of credence" would do the trick.

Eisenhower may have established a record among presidents in numbers of ambassadors (12) he kept waiting. Uneasy about just how official their status in Washington was, the ambassadors watched newspapers for signs of Ike's recovery. Heartened by pictures of him trying out a new tractor at his Gettysburg farm or playing bridge with cronies at Key West, the envoys began asking when they would be able to meet personally with the president. Back came word that they wouldn't - their accreditation was complete.

There is no published record of any international protest incidents, but there are reports of ruffled foreign feathers. In a rush to smooth them, the State Department decided that the president should host a White House lunch, a solution which helped a little, though not completely. Until the day most of them returned home, the ambassadors never quite trusted the validity of their own accreditations.

If some ambassadors have had long waits, consider the poor ambassador-designate whose government falls before he can present his credentials as happened to the ambassador from Dominica this spring. Or whose country goes to war, as Pakistan's did in 1971.

"When I pressed the State Department as to when I could present my credentials to President Nixon," the Pakistani ambassador said later, "I was told I would have to wait until a total of five new ambassadors had arrived."

It was the occasion's ceremonial aspects that Nixon relished most and, perhaps, thinking an envoy's family might share his delight, he invited wives and children to attend though he set an age minimum of five years.

He also ordered out his palace guards to trumpet the diplomat's arrival by flag-flying limousine through the southwest gate of the White House, then sent him off through the north protico to the accompaniment of the fifes and drums.

In between, split-second timing called for Nixon to enter the Blue Room from one door and the ambassador from the opposite. After posing for photographs, they slipped off to the Red Room for their five-minute chat.

Gerald Ford dropped the drums but kept the trumpets. And Jimmy Carter cut the trumpets and brought back the families (lowering the age minimum to babes in arms). He also moved the ceremony to his Oval Office.

"So exciting," said Zbigniew Brzezinski, adviser to the president for national security affairs, the other day as he stood cooling his own heels, ready to take part in Carter's talks with the ambassadors.

Less exciting, certainly, than the beginning days of diplomacy when envoys from foreign lands often were eaten before they had a chance to deliver their messages. Eventually, somebody came up with the idea of letting the emissary deliver the message first.

"From the viewpoint of the envoy himself," former Indian Ambassador to the U.S. Nani Palkhivala recently told a Bombay audience, "this was not much of an improvement."

From the viewpoint of modern day emissaries like Paklhivala ("I was lucky enough to be able to come back alive," he told fellow Indians), better to cool heels than hang by them. CAPTION: Picture, Venezuelan Ambassador Chiriboga, accompanied by family, presenting his credentials to President Carter, by Frank Johnston - The Washington Post