Washington is to ambassadors what Houston is to heart surgeons, Milan is to fashion designers and Zurich is to bankers. Some ambassadors posted here are career diplomats, survivors of apprenticeships in places like Lagos and Islamabad, who now nurture dreams of becoming foreign minister in the next cabinet. Others have been sent to Washington as a reward for a lifetime of political service or because their brother-in-law came out on top in the recent coup.

Embassy parties and the other ritual events of ambassadorial life may be impressive, but they are also as insubstantial as nouvelle cuisine. An ambassador must be a cross between Conrad Hilton and Toots Shor, playing host to every visiting dignitary from the minister of fisheries to the leader of the opposition party. Diplomatic dinners are often designed to impress these visiting firemen, not to win the hearts and minds of the American guests.

In contrast, the substantive work of a major ambassador can be as arduous as it is intangible. Months, even years, can be spent disputing the same arcane points with the State Department. Final decisions rest with the foreign ministry back home, yet, if things go awry, the ambassador is often blamed. Discretion is prized and a good ambassador leaves no marks.

Within this closed diplomatic world, few ambassadors are as effective, unusual, or take their responsibilities more seriously than Bernard Vernier-Palliez, the French ambassador to the United States. Since before Talleyrand, the French have believed diplomacy far too serious to be left to amateurs. Yet Vernier-Palliez is not a career diplomat, but an industrialist widely praised for revitalizing Renault, the state-owned auto company. In late 1981, after 37 years at Renault and six years as its chairman, Vernier-Palliez was about to fade into graceful retirement in the French countryside when he was suddenly offered his nation's plum diplomatic assignment by a new Socialist president whom he barely knew and never supported.

"It wasn't a hard decision," the 64-year-old Vernier-Palliez recalled. "Major decisions in my professional life, they are difficult, but decisions in my own life, they have always been easy." His wife, Denise, the daughter of Charles Pathe, the pioneer of French silent film, revels in at last escaping from the for-men-only world of the Parisian business elite: "Women in France --as far as business is concerned--are not involved in their husband's life at all." She called coming to Washington "absolutely an enormous chance to be offered at my age--at our age--a completely different life."

Tall and distinguished, with a smile that is almost blinding, Vernier-Palliez is known in Washington as "Sonny," an incongruous nickname that he was given by an English nanny as a child. He can be brutally candid in explaining French policy: "We have no shame at all in exporting arms." But he also complains that "diplomacy seems to be a lot less discreet than business." He can be as reserved and shy in private as he is charming in public. Awarded the prestigious Medaille de la R,esistance for his bravery during World War II, he dismisses talk of that period: "It's past history . . . It was a very common experience."

The flap over the Soviet natural-gas pipeline and the strained personal relations between Ronald Reagan and Francois Mitterrand made 1982 a trying year for Franco- American relations. Yet at the State Department, Vernier-Palliez is considered one of the most effective European ambassadors. "I have a great deal of admiration for him because he's open and direct and a hell of a good advocate for his country's position," said Undersecretary of State Lawrence Eagleburger. "Because of his nondiplomatic background, he tends to say what he thinks, and that's rare." Another State Department official added, "He's very quick on his feet, always able to defend his position and will not take implied criticism of France lying down."

Dinner at the residence of the French ambassador, an imposing 1920s chateau on Kalorama Road, is one of the brightest evening stars in the firmament of social Washington. Two or three evenings a week, the 18th-century cherubs on the dining room wall, painted in the rococo style and originally commissioned by Madame Pompadour, gaze down on a room filled with Washington dignitaries.

On a typical Monday in late January, Vernier-Palliez and his wife had 48 to dinner (including Chief Justice Warren Burger, Attorney General William French Smith, lawyer-lobbyist Robert Strauss and Washington Post Chairman of the Boord Katharine Graham) to honor Robert Badinter, the visiting French minister of justice. The dinner, which began with cocktails at 8 and ended with brandy and cigars at 11, went off with the clockwork precision of a space launch. The ambassador's toast, delivered in slightly accented English with a distinct British intonation, was graceful, apt, non- controversial and eminently forgettable. The evening displayed the grandeur that is France, the artistry of embassy chef Francis Leyerle, the gracious hospitality of the ambassador and his wife and the stiff formality of social ritual in Washington.

(These stylized dinners can daunt the uninitiated. Just before Thanksgiving, Nunzio Palladino, the chairman of the Nuclear Regulatory Commission, was expected to give a toast at a dinner welcoming French nuclear officials. Instead, Palladino, without rising, told a rambling story about an American tourist who was mistakenly arrested as a streetwalker in Paris. Vernier-Palliez and his French colleagues displayed their savoir faire by smiling politely throughout this unusualltale.)

Vernier-Palliez is far more than just a gracious host, an artful composer of diplomatic toasts and an elegant emissary from socialist France. Trying to understand his job by attending these diplomatic dinners is like trying to decipher pro football by watching only the half-time show during the Super Bowl. A far better place to glimpse Vernier-Palliez at work is at the weekly Wednesday afternoon senior staff meeting at the French Embassy on Belmont Road.

As ambassador, Vernier- Palliez presides over a huge embassy staff of about 300 in Washington. The French diplomatic contingent sprawls over a host of offices in downtown Washington and won't be united in one building until a new chancery on Reservoir Road opens in mid- 1984. As one senior French diplomat explained, "The embassy here is the mirror image of the French bureaucracy." The ambassador's management style is to delegate authority and to define clear responsibility. When he was appointed, Vernier-Palliez selected career diplomat Claude Harel, then French ambassador to Jordan, as his second in command in Washington. Harel, among his other responsibilities, handles the cables--approximately 15 a day--to Quai d'Orsay, the French foreign ministry.

No decisions are made at the embassy's Wednesday staff meetings. But Vernier- Palliez runs the meetings with crisp efficiency. The sessions are gravely formal. There is little banter or byplay and no trivia--just 16 French diplomats, reviewing the issues of the day, seated around a long conference table covered in green baize. On Dec. 1, for example, the items discussed during the 90-minute meeting included: Sen. Edward Kennedy's withdrawal from the presidential race, the situations in Lebanon and Poland, the briefing papers needed to prepare Paris for an upcoming visit by Secretary of State George Shultz, the projected size of the American budget deficit and French nuclear strategy in light of the MX missile.

When the presentation on nuclear weapons droned on too long, the ambassador, with a brief word, cut it off completely. But asds to soon as the discussion turned to the American economy, Vernier- Palliez stopped fiddling with his eyeglasses, dropped the grave mask from his face and leaned forward in rapt attention. After the embassy's financial counselor gave a brief overview, Vernier-Palliez offered a vivid account of his own conversations with Treasury Secretary Donald Regan. It was a small illustration of a larger truth: the French ambassador is better briefed and has a better understanding of American economic policy than many members of Congress.

This knowledge has been hard won. Vernier-Palliez's business ties with the United States date back to the late 1940s and climaxed a few years ago when Renault, under his direction, acquired substantial stakes in American Motors and Mack Truck. Prominent New York financier Felix Rohatyn represented Renault in both these negotiations, and he and Vernier-Palliez (known in business circles as "V-P") became close friends. The two families regularly attended the Salzburg music festival in Austria together.

"His appointment as ambassador was a master stroke by President Mitterrand," Rohatyn said. "V-P knows American business, knows how we think and knows how concerned we were by a socialist government in France." According to both the French and American press, Vernier-Palliez was appointed ambassador as a way of reassuring Americans about the Mitterrand nationalization program. Renault had been state-owned since World War II, but Vernier- Palliez ran it as aggressively as any private company. "As an executive, V-P was absolutely first rate," said Rohatyn. "In terms of his management, in terms of his negotiating skills, I thought he was terrific."

Many diplomats talk about the economy, but Vernier- Palliez is unique in regularly inviting the key players to dinner. Every two months, about a dozen major figures --from both inside and outside the government--come to Kalorama Road to draw a portrait of economic trends for their French host. The dinners are informal and freewheeling. No stiff presentations or ponderous speeches, just an evening of serious talk about the economy. Martin Feldstein, the chairman of the council of economic advisers, is a regular, as are Rohatyn and Anthony Solomon, the president of the New York Federal Reserve Bank. In addition to the conversation, the meals themselves leave a lasting impression. Listen to Nobel Prize laureate Lawrence Klein of Wharton Econometrics reminisce about the dinner he attended in November: "It was a great meal. The ambassador really has a great chef. The lamb was cooked to the pink of perfection."

Although Vernier-Palliez formally presented his credentials to Reagan in February 1982, modern-day ambassadors rarely operate at this rarified level. Asked in early December, for example, how many times he had conferred face-to-face with Secretary of State Shultz, Vernier-Palliez ticked off their four meetings on the fingers of his right hand. (However, the French ambassador did sit in on a number of sessions in Paris with Shultz, Mitterrand and French Foreign Minister Claude Cheysson in mid- December.)

The French ambassador's closest ties are with Undersecretary of State Eagleburger: "With Larry, we get along very well together. We're very direct, both of us." The mutual respect that unites the two men represents the strongest day-to-day link between the two sometimes fractious allies. Most substantive work between the two governments takes place in Washington, not Paris. The word at the State Department is that this is partly because of Evan Galbraith, the outspokenly conservative international banker whom Reagan appointed ambassador to France. "There is a much greater tendency to talk to Sonny here in Washington because Galbraith is in Paris," said one State Department official.

Even in this age of instantaneous global communications, an ambasssador like Vernier-Palliez can have broad authority to negotiate diplomatic agreements. A prime example was the French decision to join in the second peace-keeping force sent to Lebanon after the mid-September massacre in the refugee camps outside of Beirut. The United States took the lead, but French and Italian participation was considered vital.

Shultz and Cheysson had talked by telephone about a second peace-keeping force following the assassination of newly elected Lebanese President Bashir Gemayel. But a few days later, as a horrified world learned of the massacre, French negotiating responsibility rested with Vernier-Palliez here in Washington. The ambassador was summoned to the State Department at 10 p.m. on Sunday, Sept. 19, to meet with Shultz. "We started discussing the formation of a second multinational force," Vernier- Palliez recalled in typical laconic fashion. The next day Vernier-Palliez endured an arduous round of negotiations with Eagleburger and Assistant Secretary of State Nicholas Veliotes. (The Italians were in the background.) "We had to agree on a package that we could sell to our superiors," the French ambassador explained. It worked. By late that afternoon the new peace-keeping force was a reality.

The low point for the French ambassador came just two months later. The triggering incident was Reagan's Nov. 13 radio speech lifting the sanctions against the Soviet natural-gas pipeline. But for Vernier-Palliez, the real problems were in Paris, not Washington. He claims to be nonpolitical: "I am not the ambassador of a government, I am the ambassador of my country." But, at times, even a good ambassador can be undercut by squabbling politicians back home.

When the Elys,ee Palace (the home of President Mitterrand) and the Quai d'Orsay began sending conflicting signals to the Reagan administration, Vernier-Palliez was buffeted like a weather balloon caught in a squall over the Atlantic. As a State Department official explained, "I know he's being very accurate about reporting what he's told, but Sonny may suffer from the same disadvantages as other ambassadors whose foreign ministers and presidents don't get along."

The storm damage--mostly to Vernier-Palliez's pride--was minor and reportedly repaired when the ambassador returned to Paris for consultations in mid-December. But a few incidents illustrate the pitfalls that can await even the most careful emissary between two proud and prickly nations. Listening to Reagan's speech, Vernier-Palliez was shocked to hear the president make claims about allied unity that were "absolutely contrary" to the French position he had presented at the State Department the day before. When the ambassador tried to dispatch Claude Harel to the State Department to register a protest, Deputy Secretary of State Kenneth Dam refused to see the French diplomat. A few weeks later, Vernier-Palliez was still smoldering over this affront to French dignity: "It's fortunate that we're not at a time when something like this could lead to war, like with Prussia in 1870." A State Department official said Vernier-Palliez was "very embarrassed" by the whole situation, and another diplomat noted, "For a couple of weeks after the incident, Sonny kept a low profile in Washington."

For his part, Vernier-Palliez claims to be comfortable with the reality that a modern-day ambassador is an interpreter and an intermediary, not a policy maker. "When I had decided to retire from Renault," he said in January, "I had decided not to make any more big decisions. There are some who need decision-making like a drug and can't live without it. I've made decisions for a long time in my life. I don't need it anymore."

But there are other moments when one can hear a wistfulness in his voice as he talks about the differences between building cars and building bridges between nations: "In business, you make decisions that will affect thousands of people, and in a short time you show the results--for good or bad--on the last line of the balance sheet. But an ambassador doesn't make decisions like that. There are so many external events, so many other players, that it's hard to know who's responsible for what."