Buzzers erupting and electric stars blinking to life just behind his head failed to ruffle the congressional staffer as he softly discussed foreign policy and his experiences abroad. A startled visitor, even more recently arrived in Washington, asked about the clamour in the cafeteria, which the Capitol Hill aide scarcely noticed.

"It's a roll-call vote that doesn't involve me," he explained. "It's just like the time I moved into an apartment beside the biggest mosque in Beirut and was awakened at 5 a.m. the first day by the muezzin wailing prayers. You're sure that it will drive you around the bend; by the third day, you don't even hear it anymore."

The contrasts and comparisons that etch themselves onto the senses of Americans who return home after long stays abroad are perhaps sharpest here in Washington, home to an officialdom that resembles foreign bureaucracies and administrations in outward form but which maintains its own distinctly American flavor.

That flavor can be sampled in the corridors of office buildings that house the mighty, in daily newspaper headlines and at presidential press conferences. Despite the years, distance and recent turmoil, there is still a trace of the mixture of the informality and seriousness of purpose of the frontier in this town, when compared with its European counterparts. That mixture sets Washington apart as the Potomac Omphalos, the navel for the world, as the ancient Greeks would have it.

For anyone accustomed to the rigid centralization of European and Third World societies where official decisions are set in concrete the moment they are uttered and are rarely challenged, a headline announcing that the Supreme Court has been called in to uphold an Arlington parking ban is a stunning reminder of the suppleness, responsiveness and, in a sense, vulnerability of the multi-tiered American government.

"In America it is fascinating to see diplomats and journalists debating who really made such and such a decision on a policy matter," says a European diplomat from one of those highly centralized countries. "At home, you always know who makes the decision. A few people make them all."

Stroll through the White House working area and along the corridors of the Old Executive Office Building and you will notice the same kind of security and ornateness that marks palaces like the Elyse or the Quai d'Orsay in Paris.

But listen rather than look. The banter between bosses and secretaries in some National Security Council or State Department offices will tell you that you are home from precincts where chill formality and the national heritage of rigid class systems color relationship all along the hierarchy.

In some African countries, clerks and secretaries actually tremble as they approach the desks of even minor bureaucrats. Rather than risk that kind of unsettling experience, they routinely block or lose proposals and paperwork intended to be sent up the line.

In Europe, management by instilling fear in subordinates is far more subtle, but still practiced. A newcomer to Jimmy Carter's Washington is impressed with how much time Very Important People seem to spend cajoling and flattering their "support systems" into swinging into action.

The contrasts and comparisons chase each other most tantalizingly at the summit, in the public personages presented by a leader like the aloof aristocrat who is president of France, Valery Giscard d'Estaing, and of Jimmy Carter, Citizen President.

Giscard holds just two news conferences a year in contrast to Carter's twice-monthly schedule. But the French presidential news conference is an extended presentation that dwells in quiet elegance at the Elysee palace.

The 400 or more reporters who attend hand in their personally addressed invitations to the maitre d'hotel, who stands resplendent in black tie beneath the glided crystal chandelier at the entrance. Then they pad their way along thick carpet to the tapestry-lined presentation room, where Giscard soon positions himself on a Louis Quinze chair, behind an empty desk, and proceeds to light up the room with the kind of verbal pyrotechnics and agility of the French-revere.

The national compulsion of "centralizing," now being denounced in books and articles as the cause of France's administrative illness, is immediately apparent as Giscard announces to the group the general topics on which he will take questions and the time limit for each general subject.

As questions rise from the floor - invariably preceded by lengthy preambles that give the questioners a chance to demonstrate their erudition, political disagreement with Giscard or desire not to lose their jobs in the government-controlled television and radio setup - Giscard groups the queries under his general headings before starting to answer.

This gives him a chance to launch into 10-minute verbal essays on each sub-topic he chooses. In the course of the well-tailored extended explanations the most troublesome specific questions often get buried or somehow overlooked as Giscard briskly tapdances his way through the political thickets.

For an hour and a half, or longer, Giscard demonstrates that his objections at a news conference do not differ from those of de Gaulle and Pompidou. They are to dominate his questioners intellectually, to perform so crisply and articulately that the national quota of drama is met for the day, and to ignore what is not immediately useful to him.

American Presidents appear to approach news conferences much more on the run. For Richard Nixon after a certain point, the object at a news conference was merely to survive. To an untutored eye, Jimmy Carter seemed to perceive his role at last week's news conference as responding rather than dominating, of proudly tutoring the nation on some points he has recently mastered and of using television to convince the public that power has not gone to his head.

In a competitive, free-enterprise clamor that would have been put down by riot police at the Elysee, the 120 media persons in attendance jumped to their feet and shouted for recognition as Carter erectly surveyed the small auditorium in the Old Executive Office Building. It clearly had been chosen and outfitted to emphasize the businesslike, cost-efficiently nature of Carter's rule.

For someone who had not seen him in action since the first television debate with Gerald Ford, which was beamed overseas, there was a striking similarity between candidate Carter's unease in the first 10 minutes of that debate and President Carter's tense approach to the opening of a routine news conference. His body language was as expressive at times as the words he used.

His left hand charted the course of the gathering. At first it remained tensely pinched on the edge of the presidential lectern. As he turned to sensitive or potentially embarassing subjects, like details of a new strategic arms limitation agreement with the Soviet Union, his left hand automatically darted 14 times into his trouser pocket. As he dealt with a question for which he had been fully prepared and which gave him a chance to display a measure of famed humility, the left hand reappeared at the side of the lectern, fully extended and comfortable.

There was a soft pride in his voice as he recited the problems of Namibia and Zimbabwe, the African nationalist names for South West Africa and Rhodesia. And Carter was clearly pleased when he could slip back into the carefully modulated tones he used during the campaign to tell the American people of their goodness and his sincerity.

"The Mideast question is maybe a thousand years old or more, but we are working hard to try to sole it under the most difficult of circumstances," he said in the aw-shucks tone that Europeans still have difficulty comprehending.

"I think we have a lot to be proud of in this country," he said later, again in a rare moment of total ease. "There is an inherent optimism in our country."

There would have been little point in Carter's attempting to develop extended intellectualizations a la Giscard, since the American format mandates an abrupt cutting off of questions after about 30 minutes.

Moreover, they are different men, in different situations, and most of all in different countries that express national character in their own public rituals and settings. For an American coming home, those rituals offer a chance to see, and appreciate profoundly, the incomparable vitality and diversity of this country.