The world got perhaps its most revealing glimpse yet today of both the smile and the iron teeth of Mikhail Gorbachev as the new Soviet leader displayed his mastery of the western-style news conference and a certain disdain for western-style values.

Held in the gilded ballroom where the late Gen. Charles de Gaulle made some of his most startling pronouncements, today's occasion provided an insight into the views and reactions of a man who could be in charge of one of the superpowers for a generation. On display were the qualities of toughness and flexibility that propelled the 54-year-old Gorbachev to power in the Kremlin.

The iron teeth flashed when the Kremlin boss brushed aside an American journalist's question on Jewish emigration and political prisoners. "Please don't let me hear any more of this," he said sharply, insisting that he had already answered the question for French television.

Equally ruthless was his reply to a Dutch correspondent who wanted to know the total number of Soviet SS20s. "Your government has been informed of our proposals," Gorbachev shot back. "That's enough for the Netherlands."

The smile was evident in the way the Soviet leader laughingly tried to deflect a torrent of questions toward French President Francois Mitterrand who was sitting beside him on the podium. His simple, straightforward language and store of peasant aphorisms seemed vaguely reminiscent of the style adopted by the late Nikita Khrushchev.

Behaving at times as if he was addressing a political meeting in Moscow, Gorbachev showed flashes of earthy humor, righteous indignation and carefully controlled anger as he fielded questions from several hundred journalists from all over the world for well over an hour.

The alternating moods of the Soviet Communist Party chief reflected the carefully planned strategy Moscow has adopted in the run-up to next month's summit meeting with President Reagan in Geneva. Gorbachev managed to convey a combination of optimism in the possibility of a renewal of East-West detente with warnings of a grim future if the United States and the Soviet Union fail to conclude new agreements on nuclear arms.

The performance -- the public relations highlight of Gorbachev's first visit to the West since becoming Soviet leader -- also demonstrated that President Reagan now has a formidable challenger for the title of "Great Communicator".

It was former Soviet foreign minister Andrei Gromyko who caught the affable and tough qualities of Gorbachev last March during the Soviet Union's moment of transition to the new leader. "This man," he told his colleagues in the Kremlin leadership, "has a nice smile but he has iron teeth." That description seemed particularly appropriate today as the new Soviet leader showed that he is ready to be more forceful than his immediate predecessors in defending what he considers to be his country's legitimate interests.

One the most interesting insights into the attitudes of the youngest Soviet leader since Joseph Stalin came when Gorbachev was asked about encroachments by Moscow into the U.S. sphere of influence in the Middle East. The question provoked a torrent of indignation that seemed to reflect both a Russian inferiority complex and a burning desire for an equal say in world affairs.

"Americans may feel that they have vital concerns here, there, and everywhere but they should think about the implications of this . . . If you think that everything around the world is of a vital interest to yourself, what is left over for the other 200 odd states? Is the rest of the world to be a vassal of one state?" he asked.

"We are serious people in the Soviet Union," Gorbachev said, going on to ridicule western talk about "the far-reaching arm of Moscow" whenever the Soviet Union supported "progressive" movements and causes around the world.

Watching Gorbachev in action over the past few days, it has been difficult not to be impressed by the sense of quiet authority he exudes. It is expressed in subtle ways: the soft, authoritative voice; the deferential attitude of his aides; even the way he stands, feet slightly apart, like a boxer ready for a new sparring partner.

At today's press conference, it was instructive to look at the faces of the senior Soviet officials who accompanied Gorbachev to Paris. Gone were the poker-faced gazes that used to be standard issue for Kremlin bureaucrats. Their expressions were animated and alive as they sat on the edge of their chairs, evidently wondering what the general secretary was going to come up with next.

There were moments, when Gorbachev responded to criticisms on human rights or made a clever point about the arms negotiations, when the apparatchiks seemed metaphorically transformed into fans or sports coaches, egging their man on from outside the ring.

It was interesting, too, to see the issues that made Gorbachev tick. On the content of his talks with Mitterrand, and explaining his reasons for coming to Paris, he was calm and factual. When he started talking about arms control and the negotiations in Geneva, he suddenly became excited, rapping his fists on the table.

The Reagan administration, Gorbachev complained, has had a tendency until now to dismiss automatically any Soviet arms control initiative. To illustrate this point, he told a story about a peasant, his grandchild and a donkey. When the grandfather rides the donkey, he gets criticized for making the small boy walk. Whereupon the boy rides the donkey and is attacked for letting his grandfather walk.

Tired of all the criticism, both the peasant and the grandchild (whom Gorbachev seemed to equate with the long-suffering Soviet Union) decide that the only solution is for them to carry the donkey.

Gorbachev's handling of the press conference, and his public statements while in Paris, underscored the extremely clear objectives set by the Soviet leader for his first western foray. The entire trip has been carefully constructed to make as large an impact as possible on public opinion in Western Europe in advance of the Geneva summit.

The press office at the White House would admire the way the Kremlin's public relations men managed to provide a headline and an angle for every day of the visit. Wednesday, the day of his arrival, saw warnings of the "flames of war" allegedly posed by Reagan's strategic defense initiative. This was followed by the ceremonial unveiling of the new Soviet "peace plan" yesterday and Gorbachev's first western-style news conference today.

By comparison to the well-oiled Soviet publicity machine (embargoed texts in three languages, briefings by spokesman Leonid Zamyatin), the French government's media arrangements have seemed distinctly creaky. Soviet officials have also expressed disappointment at the low-keyed treatment of the visit by the French press in contrast to the page one stories elsewhere.

The Gorbachev "charm offensive" has been conducted like a military operation. Junior Soviet diplomats who would have done their utmost to avoid western journalists just a few years ago now actively seek them out.

One of Gorbachev's main weapons in this public relations offensive is his personable wife Raisa. The present visit has seen her deployed with considerable effect, posing for photographs with fashion models and looking at the French impressionist paintings in the Jeu de Paume.

Visiting the fashion house of Yves St. Laurent today, Raisa displayed her husband's talent for driving a hard bargain. Presented with a big box of St. Laurent's latest perfume, Paris, she commented: "Oh, I heard you make another perfume called Opium."

The staff took the hint and hurriedly produced an equally large gift-wrapped box of Opium.