The applause for Mikhail Gorbachev this week will be so loud that observers may overlook the fact that the new Soviet leader's performance, thus far, has been quite modest.

At the 27th Communist Party congress that opens in Moscow on Tuesday, Gorbachev will declare that, despite serious difficulties at home and abroad, things are getting better. He will make innovative-sounding proposals on domestic and foreign policy. The party faithful will voice resounding approval for his leadership.

Gorbachev-watchers in the West probably will be only slightly less restrained in their praise for the new Soviet leader. Commentators will credit Gorbachev for his bold policies, compare his reformist ideas to those of the late Nikita Khrushchev and warn that the Soviet party chief poses a vigorous new challenge to the United States, both as a partner and a rival.

But Gorbachev's performance doesn't yet merit this chorus of congratulation. For there is less to the general secretary's international momentum than meets the eye.

Gorbachev's successes thus far mostly have been in two limited areas: personnel and public relations. He has proved adept at both, placing his supporters in key positions and presenting a fresh young face to the Soviet and Western publics. But these are largely procedural accomplishments, triumphs of style and political cunning rather than substantive policy.

Beneath the public-relations veneer, Gorbachev faces the same problems that troubled his predecessors: a feeble economy, a fraying empire, a restless population. These problems haven't improved since Gorbachev's accession to power, and in some cases they have gotten worse. More important, Gorbachev hasn't shown any willingness to consider the fundamental changes that might improve the Soviet position.

Consider Gorbachev's paltry record:

The Soviet economy, rather than improving under Gorbachev's supposedly dynamic leadership, remained sluggish last year and in some important areas actually declined. National income rose 3.1 percent, a slight gain over 1984 ut less than the average annual increase of 3.2 percent over the last five years under Brezhnev, Andropov and Chernenko.

Soviet foreign policy under Gorbachev has produced much noise but little benefit for Moscow. U.S.-Soviet dialogue, resumed by his predecessor Konstantin Chernenko, hasn't borne any fruit other than a get-acquainted summit. President Reagan's commitment to the Strategic Defense Initiative appears unshakeable. Attempts to build separate bridges to the West Europeans at the expense of NATO cohesion haven't gone very far. The Chinese and the Japanese remain suspicious of Soviet overtures. The situation in Eastern Europe is under control for the moment, but the potential for turmoil is as great as ever. And in the Third World, the Soviets are confronted by U.S.-backed counterinsurgencies against some of their clients, which raise the costs of Soviet empire.

Gorbachev, the supposed innovator, in fact appears to suffer from the same insecurities, anxieties and rigidities that have hindered Soviet foreign and domestic policy for decades. At a time when the Soviet economy cries out for basic reforms, he appears wary of tampering with the system of state socialism created by Stalin. Abroad, he continues to depend on the same motley array of clients: Angola, Ethiopia, South Yemen, Vietnam, Cuba, Nicaragua.

The weakness of Gorbachev's performance is masked by his public-relations skill. The general secretary is now routinely described as a great communicator. British Prime Minister Margaret Thatcher said that she could conduct business with him. And after the Geneva summit, President Ronald Reagan publicly vouched for "the sincerity" of the Soviet leader and later expressed thanks for his arms-control package, which one administration official described as "breathtaking."

But spectacular imagery is not a substitute for cutting through the web of foreign and domestic problems in which Moscow has become increasingly entangled during the last ten years. And with the exception of nuclear arms control, Gorbachev hasn't given a hint of any intent to reform the familiar Soviet world outlook.

Because Gorbachev made so few changes in Soviet policy, outside the arms-control arena, during his first year in power, one must look to his team of advisers for clues about his intentions. For if the new general secretary is quietly masterminding a shift in Soviet international conduct, he should already be putting in place a cadre of like-minded associates.

But the Gorbachev team is far from innovative. His appointees are younger and more public-relations oriented, but they have shown show little desire to break with the established pattern of Soviet international behavior.

Gorbachev's chief political deputy is the tough provincial secretary from Tomsk, Yegor P. Ligachev, 65. A protege of the late Mikhail Suslov, for decades the protector of Communist orthodoxy, Ligachev has already impressed the foreign communists who have encountered him as a hard-nosed ideologue, suspicious of change.

Addressing the Cuban Communist Party congress several weeks ago, Ligachev emphasized the continuity in Soviet policy under Gorbachev: "I would like to stress that all our plans, perspectives and tasks are based on the accomplishments of our society during all the years of the Soviet authority." That doesn't signal enthusiasm for major domestic reforms.

As his new foreign minister, Gorbachev picked Eduard A. Shevardnadze, 57. Like Ligachev, he lacked any international background when he took office. A former police chief and party functionary from the southern republic of Georgia, Shevardnade appeared to be a risk-taker and relatively open to new ideas, by the standards of the Soviet bureaucracy. But his inexperience, his background as a problem-solver rather than a conceptualizer and his well-documented tendency to defer to Politburo heavyweights may prove to be a problem.

Lower-level appointments confirm this pattern of new faces but old policies. For example, Anatoly Chernyaev has replaced Andrei Aleksandrov, who has served as foreign-policy assistant to every general secretary from Brezhnev on. This change was touted as a breath of fresh air, since Chernyaev, trained as a European historian, had been popular among Moscow's liberal intellectuals, who found him unusually broad-minded and easygoing for a party official.

But old friends have noticed that as Chernyaev rose through the hierarchy, his views gradually became more orthodox. They say that he would enthusiastically praise the human qualities and intellectual faculties of the stolid Leonid Brezhnev, for whom he sometimes wrote speeches.

One aide who has Gorbachev's ear on international matters is the chief of the Central Committee's propaganda department, Aleksandr N. Yakovlev. Since he served as ambassador to Canada and is described as an Andropov protege, Yakovlev is regarded by some analysts as an innovator who inderstands the West. But several of Yakovlev's former subordinates at the Institute of World Economy and International Relations, where he worked before moving to the propaganda job, describe Yakovlev as an ideologue who -- despite his stint in Ottawa -- has a simplistic, dogmatic view of democratic societies.

Gorbachev's own public-relations savvy also has some striking limitations. U.S. officials who dealt with him in Moscow and Geneva complained about the rigidity and nearly arrogant self-confidence with which the Soviet leader would lecture Americans about their own country.

In an October interview with French television, Gorbachev asked rhetorically what would happen if workers were allowed for even half a year into Western parliaments. The question was particularly inappropriate in France, where the Socialists are in power and where dozens of Communist deputies sit in the National Assembly.

In that interview, Gorbachev claimed that nowhere else do Jews enjoy the same rights as in the Soviet Union. And in an interview early this month with the French newspaper "L'Humanite," the general secretary declared that Soviet-style censorship "exists in one form or another, in every country." He also explained that "Stalinism is a concept thought up by the enemies of Communism and widely used to discredit the Soviet Union and socialism as a whole."

This assertive parochialism is coupled with a burning desire to enhance his country's superpower status. At the April 1985 Central Committee Plenum, Gorbachev implied that one urgent reason for improving the Soviet economy was the danger of losing ground in the international competition. Fedor Burlatsky, a distingushed Soviet political commentator and a former Central Committee aide with links to Gorbachev, made the point particularly bluntly: "We have to think about the future . . . . Either we will be able to ride on it, to rule it, or other peoples and states will begin to pass us and to push us around . . . . "

Gorbachev obviously suffers from his inexperience. He made a costly gaffe at a joint press conference with French president Francois Mitterand during his autumn visit to France, when he left his host no alternative but to repudiate the Soviet proposal regarding separate talks with Paris and London on intermediate-range nuclear forces in Europe.

At the same event, the general secretary also managed to offend the Dutch, who were about to make a crucial decision on deploying American cruise missiles. He answered a Dutch correspondent's question regarding the number of SS-20 missiles with a patronizing: "Your government has been informed of our proposals. That is enough for the Netherlands."

Gorbachev's offer to separate the issue of intermediate-range nuclear systems from progress on the Strategic Defense Initiative was also clumsily presented. Moscow claimed that an agreement would require Britain and France to forego the planned modernization of their obsolete nuclear arsenals. Since Paris will surely refuse this demand, European arms-control advocates will have to blame the likely deadlock on France rather than the United States. No wonder some Reagan administration officials were openly relieved.

These incidents remind us that an excessive self-confidence may be dangerous. As one Soviet official with access to Gorbachev observed: "The general secretary is a very smart man. You start a sentence in his presence and he finishes it up for you. The only problem is that sometimes he finishes it up wrong. And few would dare to correct him."

Gorbachev's openness toward the United States may also have backfired, since it has eased the pressure on the Reagan administration to offer real concessions to the Soviets. The very fact of the Geneva summit -- with its images of Reagan and Gorbachev smiling at each other -- inevitaby created an impression in the United States that Reagan's hard-line policy toward Moscow had worked and forced the Soviets back into serious arms negotiations.

In Western Europe, the opportunities for Soviet public diplomacy are greater. Unfortunately for Gorbachev, he came to power three years too late. If the Soviets had displayed half of his flexibility on intermediate-range nuclear weapons before the first American missiles were deployed, European public opinion would be rallying massively behind his initiatives.

But the missiles are being installed without much trouble, Reagan has become more sensitive to allied perspectives on East-West diplomacy and there is no sense of urgency in Europe to cut a deal with Gorbachev. Moscow's continuing heavy-handed treatment of West Germany mars the Soviet image in Western Europe as well.

The Kremlin hasn't been much more successful in the Far East. Shevardnadze's January trip to Tokyo revived Soviet-Japanese dialogue, but accomplished little else. The Chinese, despite sweet approaches from the Soviets, have refused to consider a non-aggression pact as long as Moscow continues its intervention in Afghanistan, supports the Vietnamese occupation of Kampuchea and remains unwilling to reduce its forces on the Sino-Soviet border.

In Eastern Europe, where Gorbachev's appointment was received with hope, he has also encountered difficulties. Moscow is trying to put the East Europeans on a shorter political leash. But it also wants to stop subsidising them. Indeed the Soviets want the East Europeans to contribute to Soviet economic development. To stay afloat, however, the East Europeans need a combination of domestic economic reforms and cooperation with the West -- precisely what the Kremlin finds undesirable.

These foreign problems are all compounded by the weakness of the Soviet economy, which advertises the failings of the Soviet system and forces painful political decisions about how to allocate scarce resources.

The economic crisis may even be getting worse. Economist Jan Vanous explains in the latest issue of his newsletter PlanEcon Report: "Contrary to the general impression conveyed throughout 1985 in the Soviet economic press and emphasized by Western media, Soviet economic growth did not accelerate in response to the more dynamic leadership of Gorbachev and his program of improved economic discipline."

Vanous adds that according to his own estimates of Soviet production during 1985, it's possible that "Gorbachev presided over the second-slowest growth in post World War II Soviet economic history."

Because the Soviet model of development has lost nearly all its worldwide appeal, Gorbachev's foreign policy will continue to be based on bayonets. Smiling at the same time won't provide a long-term solution.

That Gorbachev cannot walk on water is no reason for complacency in Washington. Even under his inept predecessors, the Soviet superpower had a major impact on the world. But the Reagan administration until recently could be confident that Washington's diplomatic blunders would be more than matched by Moscow. The free ride is over. Gorbachev demonstrated his skill at public diplomacy most recently by accepting the principle of on-site inspection -- removing at a stroke the Reagan administration's most convenient excuse for avoiding arms-control agreements.

The general secretary has the potential to grow on the job. Gorbachev still may not be sure how far, how fast and in which direction he will take the Soviet Union. At this early stage, dismissing the Soviet leader is as foolish as portraying him larger than life.

But Gorbachev will have to make tough decisions and major policy shifts before the current Soviet decline is reversed. The delegates at this week's Party congress in Moscow shouldn't hold their breath.