Poised between menacing Soviet tanks and strongwilled striking workers, Poland's Communist Party chief Edward Gierek is walking a brink he has come to know well.

Thrust to the forefront of Polish politics a decade ago by worker riots, the 67-year-old communist leader was seen as representing a transition from the old-line ideologists -- notably his authoritarian predecessor Wladyslaw Gomulka -- to a highly pragmatic and technocratic-minded party elite.

Yesterday's shakeup of the party's ruling Politburo and the bargaining concessions made by the Warsaw government were major gambles by Gierek, in effect leaving no one left to fire but himself, should these moves not succeed in ending the strikes.

From the start of the crisis, Gierek has tried to steer a difficult course to appear flexible enough to appease the strikers and yet firm enough to convince Moscow that he is not condoning anything that would undermine the fundamental principles of the Soviet Bloc.

Being Polish party chief has never been an easy job. Under the inhibiting gaze of the Kremlin, Gierek has shown himself to be a skillful political straddler.

He has maneuvered his restless nation along a path of sputtering economic gain, spurred by Western aid while permitting only very limited reform of Poland's governing system. The shortfall results of this strategy have led to the present discontent.

The crisis spotlights both the conflicts and strains inherent in Gierek's compromise approach and calls into question his ability to stay in power much longer.

Compared with other Eastern Bloc leaders, Gierek is regarded by Western observers as a realist for tolerating vigorous internal dissent and as a moderate for advocating cooperation with capitalist countries. At the same time, Moscow hails him as a faithful party chief.

This East-West balancing act has carried significant economic advantages for Poland as well as personal political gains for Gierek.

The Polish chief's courting of the West for modern technology and financial credits brought more economic progress to Poland than is sometimes appreciated. It has also helped Gierek's popularity with many Poles who like to see their country as a bridge between East and West.

Gierek's own understanding for the West is deeply rooted in the long spell he spent living there. His family migrated to France in 1929 following the death of his father, a miner, in a mining accident.

In France, Gierek himself, then 13, went to work in the coal mines. He joined the French Communist Party in 1931 and was expelled from France three years later for participating in a strike.

He returned to Poland, but only for a short while. In 1937, Gierek moved to Belgium, where he spent the war years working in the mines. His offical biographers say he also worked for the resistance. He returned to Poland in 1948, earned a degree in mine engineering and started working his way up the Polish Communist Party ladder in Katowice in the mining region of Silesia.

As party chief, Gierek has, built an image as one of communism's leading international statesman, an image that appears to serve Soviet diplomatic designs as well as his own.

The Polish leader, for instance, has offered to play host in Warsaw to an East-West European conference on disarmament, a proposal in which Moscow has keen interest. As if to highlight Poland's key role in detente, Warsaw was the venue last May for hastily arranged meeting between French President Valery Giscard d'Estaing and Soviet President Leonid Brezhnev, the first summit-level, East-West contact following the Soviet invasion of Afghanistan.

Yet Poland unquestionably remains solidly bound to the Soviet-led Warsaw Pact, and Gierek loses no opportunity to make clear his loyalty to Moscow. While pointing Poland west for technical knowhow and financing, he had even ruled out to date major reforms in its Soviet-style central planning system, despite its adverse effects on the economy.

Both East and West would thus seem to have a vested interest in the survival ofGierek's leadership.

Meantime, inside Poland, a country known for its expressive, independent-minded people -- the party chief has also proven himself adept at balancing influential interest groups.

He has dealt with the powerful Catholic church as a partner, demonstrating a willingness to cooperate. He has allowed more dissent from Poland's intellectual circles than would be permitted in most East Bloc countries, though harassment persists. He has shown respect for the work of technocrats, given the impression of listening to the problems of farmers, and conveyed concern for the living conditions of workers.

In general, Gierek has sought to play the role of concerned master of the house, with his main aim being to avoid confrontation.

Gierek's roots as the son of a miner and a onetime coal shoveler himself gave him extra credibility when he became national party leader in 1970. He had achieved a reputation in Silesia, his power base, as a man of the people. That he spoke a Polish miner's dialect only accented his folksy appeal.

This impression of him was strengthened during the 1970-71 strikes when Gierek talked personally with striking harbor workers in Szczecin. A personal appearance by a party chief was regarded as extraordinarily courageous and considerate.Later, he visited a number of factories, making promises of progress to come.

The same down-to-earth approach was used everywhere. He would shout to his worker audiences, "Will you help?" and they would shout back, "We will help."

As his modernization program began to show gains in personal income and living standards for Poles, in the early 1970s, confidence in Gierek's rule grew. But Poland's progress in the past five years has fallen short of the gains made in the first half of the decade, reflecting on Gierek and eroding the personal good will he had amassed with the public.

Critics both in and outside Poland have recently faulted the party chief for being too cautious and limited a reformer as well as for looking too fearfully over his shoulder at Moscow. Once seen as conqueror of the party machinery, he is now described as its captive.

Another charge against Gierek is that he has now lost contact with the people, becoming isolated in office if not ossified by the party bureaucracy. As one Pole told a recent visitor to Warsaw, the popular feeling is that no one at the top is helping anymore.

While openly acknowledging the economic trouble Poland is in, Gierek had made a point in recent years of not arousing expectations of major economic change. His message had been for Poles to face up to economic austerity and soldier through.

His speech to the Polish nation yesterday promising "major changes in the economy" may have signaled a turning point, Western analysts say. But Gierek offered no specifics, and reforms introduced in the past have been watered down subsequently to insignificance.

The intent of the Politburo reshuffling was not much clearer than the meaning of the speech. Some Western analysts see it as an attempt by Gierek to reassert control and co-opt the reform movement. But the situation in Warsaw remains unstable enough to topple Gierek.

Gierek is widely regarded by Western diplomats who know him as likeable, decent and honorable. Many still see him as preferable to a reactionary party chief who could well be installed should the current crisis bring Gierek's fall.