Despite fresh reports of increased military readiness along its Polish frontier, the Soviet Union is not pictured by analysts here as any more eager now to invade Poland than it might have been last summer when the crisis first erupted.

The drama being played out in Warsaw, Gdansk, and other major centers of political struggle in the troubled East Bloccountry still seems short of establishing the conditions under which Moscow would order its troops in.

That threshhold, it is assumed, would be crossed only if the Polish Communists lose political control and authority to the independent and increasingly fractions trade union movement. That would imply so fundamental a change in the country's political system that the Soviets would consider it to be breaking free of the socialist East Bloc.

In such an event, it is accepted here, Moscow would intervene, regardless of warnings such as it received this week from Washington and other Western capitals of catastrophic impact on the Soviet Union's trade and diplomatic relations with the West and the rest of the world. The Afghanistan invasion of last December -- rather than acting as a deterrent in the present crisis -- made quite clear that Moscow will use force to preserve what it considers its vital interests. Poland, historic buffer for the Soviet Union and vital supply route to Soviet armed might in East Germany, is of vital importance to the Kramlin as it surveys its empire's security.

What cannot be known here is how the conservative, doctrinaire old men of the Soviet leadership will react if Solidarity and the other newly independent trade unions reject the results of the latest crisis session of Stanislaw Kania's party Central Committee, fail to get back to work, threaten more strikes and make further demands.

The Polish crisis already has demanded extraordinary patience from President Leonid Brezhnev and his Politburo, who run their own country with an absolute authoritarianism that stands in sharp contrast to present-day pluralistic Poland. The Soviets have had to accept the presence of a strong Roman Catholic Church in Poland, but the appearance of strong unions able to challenge and in some cases force the disciplining or firing of party officials must cut deep into the psyches of men who themselves have never hesitated to stamp out open challenges to their authority.

The official press in the months of the turmoil has painted Poland as a country endangered by "antisocialist elements," prey to corrupting "Western imperialists." Jamming of Western radio stations has cut down sharply on general knowledge of what is going on in Poland, and at the level of the man in the street, there is both resentment of what is seen as Polish bad faith and chaos, and worry that somehow the West will entice the Poles away from fraternal solidarity with the Soviets who have scarificed so much to preserve their country.

There is little room in Soviet perspectives for worrying about such historical events as the division of Poland by Stalin and Hitler in 1939, the Katyn massacre of Polish officers on Stalin's orders, or the 1944 Warsaw uprising, when the Red Army sat idle on the Vistula's east bank while Germans decimated the Polish Home Army and then leveled Warsaw. The political and pyscholigical atmosphere of self righteous embattlement that eased the Kremlin's explanations of the 1968 invasion of Czechoslovakia are present again in the Soviet capital.

While little is known at the popular level of the dangers perceived from the Kremlin of contamination of other in East countries from the crisis, the leaders are certain to be worried deeply. It is likely that East Berlin and Prague consulted with Moscow before sharply restricting travel to and from Poland in recent weeks, and mounting stiff propaganda campaigns against Solidarity leader Lech Wales and the free unions in general.

At this or any future moment of tension, Moscow may be deterred by the certain knowledge that, unlike the Czechs, the Poles would fight any intervention. Poland's Army, with more than 15 divisions well-equipped by the Soviets, is thought here unlikely to agree to keep to garrisons as the Czech Army did. And unlike the 1956 Hungarian Revolution, the conflict would include workers and soldiers alike and pose for Moscow the problem of explaining to other East Bloc countries and Communist parties abroad how it came to make war against the workers. With 30 divisions of its own, including two in Poland, and nearly 30 more in a high state of readiness in the Western U.S.S.R. the Soviets could bring overwhelming force to bear. But it could prove a costly victory, with much blood spilled.

The West has made clear trade would all but end if the Soviets intervened, and in the long run, this may weigh as heavily in Moscow's thinking as any other factor. Soviet trade with the noncommunist industrialized world grew 26 percent in the first nine months of this year, with exports running nearly even with imports.

More than a third of the export cash is earned by oil, and Moscow has just announced major expansion plans for natural gas production to expand its energy exports at a time when petroleum exploitation is facing severe new problems. Intervention not only would destroy massive new joint investment projects for pipelines from Siberia to West European markets, but also would make it politically impossible for any Western leader to support such deals for years to come.

Analysts here believe the Kremlin saber-rattling may have obscured the significance of the $1.1 billion hard-currency loan from Moscow that Kania announced in Warsaw two days ago. Poland faces debts in the West of more than $23 billion, and is frantically seeking about $8 billion in new loans to help service its debt and restructure its financing.