DOWN the hall from his wood-paneled study in Metternich's old living room above the Ballhausplatz, Bruno Kreisky hunches over a green felt table, removes his glasses and rubs his eyes wearily as Slavic nationalists harangue him about the need to teach Slovenian as well as German to their kindergarten children.

The day before, the 72-year-old ruler stood in Parliament for 15 hours, responding to a ceaseless flow of questions, at times with mock fury or impish insolence, from a disgruntled band of opposition legislators.

"I believe in the principle that government should not remain aloof from the people," Kreisky says, in explaining why he even encourages people to call him at home. His number is in the book. "It's very important for me to hear the everyday voices of working men and women."

When he strolls into the Oval Office today to see Ronald Reagan, Kreisky will be dealing with his fourth U.S. president since 1970. "Kaiser Kreisky," as his good friend Willy Brandt calls him, has reigned as Austria's chancellor for 13 years, in power longer than any other western leader. Largely because of his feisty iconoclasm in world affairs, Austria is no longer considered just an Alpine enclave immersed in sacher torte and cream, but an active intermediary between East and West whose voice also carries weight in the Middle East and on development issues between rich and poor nations.

Kreisky has been intimately involved in his country's role as a pivotal bridge between East and West ever since he went to Moscow in 1955 as part of a delegation that negotiated the state treaty that ended Austria's occupation since the war by the United States, the Soviet Union, France and Britain.

But he has rarely, if ever, sounded so pessimistic about relations between Moscow and Washington. "It should be possible to bridge the gap, but the superpowers can never harmonize their policies because they will always be suspicious of each other," he said in an interview at the end of another 12-hour workday. "There may be no chance of coexistence in the long run, for de'tente will always be a temporary policy based on equality of arms.

"We are entering a new era of nuclear weapons that will make war the most dangerous idea we've ever known," he said. "The deployment of Pershing II and cruise missiles [scheduled by the North Atlantic Treaty Organization to begin later this year if arms control talks fail] could mark the beginning of a new cold war."

"If Ronald Reagan were to meet [Soviet leader] Yuri Andropov next week, then I might be more optimistic about the future of arms control," Kreisky added. "A deadlock can only be resolved by a political breakthrough and not technical discussions in Geneva."

Kreisky has flouted convention ever since his youth. At 14, he participated in his first demonstration against the Vienna school system after a fellow pupil committed suicide. He soon became a militant socialist, promoted a clandestine youth movement that met in the Vienna woods and was arrested in 1935 for high treason.

He was sentenced to one year in jail. Later, when the Gestapo went after him, Kreisky was taken into protective custody and released in 1938 with orders to leave the country. He fled to Sweden, where he worked as a correspondent for several foreign newspapers and remained active in socialist politics.

In the circle of political exiles from Nazi Germany, Kreisky developed a close friendship with West Germany's Social Democrat leader, Willy Brandt. At the same time, he met and married Vera Furth, the daughter of a textile importer.

After an eight-year absence, Kreisky returned to Austria in 1946 and quickly became involved in the delicate diplomacy required to restore Austria's independence. By 1953, he had worked his way up to become undersecretary of state in the foreign ministry, launching a 30-year career dominated mostly by his long tenures as foreign minister and chancellor.

Kreisky's concept of "active neutrality" has pleased most Austrians, despite occasional complaints that he has neglected domestic affairs in favor of his impassioned involvement in foreign issues.

"He has put Austria on the map of international politics," says Paul Lendvai, a journalist who has watched Kreisky's career over the last three decades. "People enjoy the spectacle of summits and high dignitaries meeting in their capital, especially since this country long ago lost its empire."

Kreisky's stature in the Arab world and Eastern Europe, moreover, has bolstered Austrian exports. Businessmen and economic consultants often tag along on his foreign trips and find that many doors are opened because of the chancellor's forthright reputation.

Kreisky also has sought to wean United Nations institutions away from Geneva and New York by establishing a vast complex of office buildings designed to accommodate international agencies and burnish Vienna's image as a neutral capital.

At home, Kreisky has applied all the wiles of Metternich and Bismarck to keep political opponents off balance and secure his lock on power. Recently, he shrewdly disarmed attacks on his economic policy by selecting one of the opposition's most articulate economists, Stefan Koren, to preside over Austria's central bank. Thus, in one stroke, Kreisky deprived his opponents of one of their most effective voices and also won lavish public praise for his magnanimity.

An essential element in his populist approach to government, explains Kreisky, is access to the common citizen. He usually rises at 7 a.m. and settles into a long breakfast routine, interspersed with frequent phone calls from bankers, civil servants or people with serious personal problems.

The Austrian leader also feels gloomy about the world economic crisis, which he believes is already fomenting serious political turmoil in developing countries and may soon spread to western nations.

"I'm not so sure that an unemployed worker in Detroit or in Belgium is convinced that he lives in a fine society," he said. "When he asks, 'Why is it impossible for millions to find jobs?' he only hears that the present economic crisis was a destiny that could not be overcome."

Kreisky, who has served as one of the guiding forces in North-South dialogue between rich and and poor countries, believes that the West will have to awaken to the idea that its recovery may depend on the Third World because that remains the largest source of untapped markets.

"Nobody is now saying tell the poor countries to go to hell," he said. "There is a growing consensus that a joint policy will be needed between rich and poor nations, another kind of Marshall Plan if you will, to revive the world economy."

Kreisky's grave concern about East-West relations and the world economic crisis also betrays an abdication of personal interest in searching for ways to cultivate peace in the Middle East.

In his controversial efforts to probe new channels for peace, Kreisky has welcomed Libyan leader Col. Muammar Qaddafi to Austria, embraced Palestine Liberation Organization leader Yasser Arafat and found himself castigated as a self-hating Viennese Jew by the Israeli government for his espousal of Palestinian national rights.

Today, Kreisky says simply, "Israel is not ready for peace. There will have to be a change of government before any progress can be made."

Kreisky has not hesitated to call Israeli Prime Minister Menachem Begin "a semi-fascist who believes in war, in methods that are anti-democratic and in apartheid by his treatment of Palestinians inside Israel."

"The only chance for peace will come when Israel decides it must give up purely Palestinian lands, meaning the West Bank and the Gaza Strip, and give up its policy of apartheid toward the Arabs," he said.

He defends his overtures to Qaddafi, saying, "If one man can talk with him in a sensitive way, the world has a far better chance of moderating his behavior than if he is ostracized.

"Qaddafi is a revolutionary who thinks in different categories than you or me," Kreisky said. "I don't share his views--as a socialist I favor evolution. But we should try to use every opportunity available to build cooperation with the Arab world if we are going to have a dialogue to make peace."

Like many politicians, Kreisky admits that the excitement derived from power has whetted his appetite to continue in office. He is running again for reelection this April.

But the wear and tear from exercising power has taken its toll, as have a number of physical ailments that have seriously weakened him. In recent years, Kreisky has suffered from recurring eye infections, lumbago and emphysema, and now requires weekly kidney dialysis treatment. To sustain his health, he also has tried to spend more of his working days at his holiday retreat in Majorca, Spain.

"If we were prospering today, if de'tente was working, it would be easy to say goodbye," he says.

Instead, he vows to stay on as chancellor--if his party "wins a clear-cut majority" in April.