Official silence by the major governments of Western Europe over the naming of Stanislaw Kania as Poland's new leader contrasted with privately expressed concern that the decision may mean the Soviets have gained the upper hand in Warsaw.

Although Western European powers all seem to have concluded that the replacement of Edward Gierek was only a matter of time, their embassies in Warsaw were obviously surprised both by the speed of the transition and by the choice of the little-known Kania. His name had figured, for example, in none of the lists of possible successors cabled home by the French Embassy, sources said.

The initial conclusion of diplomatic observers was the Kania is a hardliner chosen at least to reassure the Soviets, if not to do their bidding.

His appointment raised questions about the future of European detente with renewed force.

The most optimistic note was struck by British sources who speculated that Kania may have been named because the Polish government is determined to carry out its agreements with the new independent trade unions and wanted to give the Soviets guarantees that the party would circumscribe the deviations from Communist orthodoxy, Washington Post correspondent Leonard Dowie reported from London.

Kania's lack of reputation abroad and foreign policy experience is one of the most disturbing factors to West European observers. They fear this means Poland will no longer be willing to be able to play its traditional diplomatic role as the most important communist intermediary between Western Europe and Moscow, a role that has made it a key element in establishing and preserving European detente.

Gierek's departure is a major blow to French President Valery Giscard d'Estaing and German Chancellor Helmut Schmidt, who in tandem have been trying to carve out a special position between Washington and Moscow.

Gierek's own special position was dramatically underlined late this spring when he arranged a meeting in Warsaw between Giscard and Kremlin leader Leonid Brezhnev that broke the Soviet diplomatic isolation after the invasion of Afghanistan.

But Brezhnev's special relationship with Gierek, the only Soviet Bloc leader formed in the West rather than in Moscow, was apparently shaken because he gave too much away to the Polish workers and also perhaps because he turned Westward for financial help out of the economic crisis that led to the strike movement.

An authoritative account of how Polish ambassadors in the West asked for aid perhaps illustrates the kinds of developments that disturbed the Soviets, even though the Polish envoys may only have been telling Westerners what Warsaw thought they wanted to hear.

The approach in a major continental capital, confirmed by the sources to have followed the same pattern in Washington and elsewhere, was for the Polish ambassador to:

Thank the Western foreign minister for his government's prudent and helpful silence about the Polish strikes.

Say that the workers' demands had been both "just and justified."

Conclude that Poland could simply not afford to honor the economic concessions in the agreements signed with the workers unless new massive Western aid is forthcoming.

The estimate given by the Polish ambassadors was that the economic parts of the deal would cost Poland $3 billion that Warsaw had not planned on.

It was apparently in response to this Polish plea that President Carter appealed to the allies to help Poland, a request that has elicited a growing debate in Western Europe about the wisdom of helping the Polish government out of its difficulties and the implications of this for East-West relations.

Even before the naming of Kania, the dominant theme in West European government circles was to wait and see whether the Polish government honors its agreements with the workers. But this prudence was accompanied by widespread official willingness to heed Carter's call to help bail out the Warsaw government.

West German banks formed a government-backed lending consortium for Poland. The nine-member European Community is ready to put together a joint aid package, "if this is required," Luxemburg Foreign Minister Gaston Thorn, the current Common Market chairman, said yesterday. m

The Paris paper Le Figaro spoke today of "a real East-West competition to help Poland overcome its economic difficulties" after Moscow had indicated willingness to lend Poland Western currencies to buy Western goods.

Only the French seem to be hanging back, perhaps because French bank interest rates are double the German level of 7.5 percent, and a French loan would need to be subsidized by the government to be competitive.

French official sources say France has already done much for Poland in the past year by stretching out existing loans. The sources refuse to give details "so as not to embarass the Poles."

Pierre Lellouche, a leading young strategy thinker at France's top foreign affairs think tank, the French Institute of International Relations, said that "the minute anyone touches a corner of the Soviet empire, everyone trembles. When the socialist system falls apart in one of the Soviet satellites, everyone pumps in dollars and [West German] marks." t

Another widely repeated interpretation of the reasons for Western willingness to aid Poland is that it is the logical conclusion to the "Sonnenfeldt doctrine." Attributed to Secretary of state Henry Kissinger's deputy, Hermut Sonnenfeldt, it held that the Soviet Union should be reassured by the West that its control of its sphere of influence is uncontested.

Pierre Hassner, one of France's top political scientists, said he was struck by the comparison between the Western responses to the crisis in Afghanistan and Poland. In the Polish case, he said there is general agreement because this time the United States accepted the West European position of doing nothing as the lowest common denominator for the Atlantic Alliance. "Are we going to help the Soviets keep control of the approaches to their fortress? It seems so. Everyone is for order."

Yet Hassner said he felt the West should use its financial leverage to consolidate the Polish workers' gains.

Similar thoughts appeared in a wide range of European publications. The West German intellectual weekly Die Zeit, the Yorkshire Post and London's authoritative weekly The Economist all questioned whether it would not be better to wait before subsidizing the Polish government.

In France, Jean Daniel, leftist editor of the weekly Nouvel Observateur, said that the Polish workers' victory "upsets everyone and is threatened from all sides . . . In Poland, as in other Eastern countries, as in so many South American dictatorships, capitalists these days make nothing but profits, and all they ask for is a very strong and stable government."

At the opposite end of the French spectrum, Jean-Francois Revel, the strongly anticommunist editor of the weekly L'Express, attacked what he called "subsidized detente" because it helps the Soviets arm themselves more heavily.

"Doesn't it furnish aid that allows totalitarian authorities to maintain themselves rather than lifting the standard of living of the people?" he asked. "Are we helping men live decently or helping governments oppress men?"

One answer to these objectives given privately by officials is that the level of Western aid so far discused only helps the Polish government service its debts and avert the potential financial disaster for the West of a Polish default.