Although Americans are "breathing more easily about Poland" these days as the prospect of Soviet military intervention appears to be receding, the chairman of the House intelligence oversight subcommittee argues that "the real danger has not passed" and is in fact, "just about to begin."

In a report titled, "The Worst Is Yet to Come," published today, Rep. Les Aspin (D-Wis.) asserts that "the chances of a Soviet invasion are very high."

Contrary to many intelligence and press reports suggesting that the Soviets completed preparations to invade Poland early in December, Aspin claims "there is strong evidence" that Moscow wasn't fully ready then, militarily or politically, and that the real danger will run from "mid-January to the end of March."

Aspin says that U.S. officials have been "touting" Soviet preparedness for an invasion since Dec. 3. "It is this official position, more than anything else," he says, "that has produced the current sense of ease."

But Aspin, whose committee has been studying the U.S. intelligence community's ability to forecast Soviet invasions such as those in 1958 in Czechoslovakia and Afghanistan in 1979, says this early forecast of readiness for a possible intervention early in December "may be another case of the common intelligence failure of mirror-imaging -- assuming that others are like us."

The United States, he argues, puts great emphasis on the "firefighter approach," where speed is important. "The Soviets give much greater weight to advance preparation." The Soviet military, he said, "is both precise and plodding." As in the cases of Czechoslovakia and Afghanistan, its procedures require six months for an invasion of this kind that preparation time won't be up until mid-January, he says.

Though the Kremlin probably still hasn't made up its mind to intervene, Aspin says, the "odds, strongly favor an invasion" and he cites three reasons.

First is what he calls "bureaucratic momentum," meaning that so much work has gone into preparations and so many careers are on the line that bureaucrats may be keenly aware they must "use or lose" this January-March "window," after which spring rains and other factors will make it hard to maintain the current forces in place.

If Poland blows up after this time and the troops are out of position, then undoubtedly there are Kremlin officials worried about "taking the heat," he says.

Furthermore, he adds, "On no other occasion of which we are aware have the Soviets failed to use the mobilized forces at their command after such massive preparations."

Aspin also says that Poland's communists today are anything but a reliable instrument of Kremlin control and that the party leader, Stanislaw Kania, faces opponents within his party who would like to see a Soviet intervention sweep him from power.

On the military side, Aspin essentially argues that Moscow's "checklist" of preparations is longer than some other U.S. analysts believe.

Czechoslovakian intelligence officers trained in the Soviet system, Aspin reports, said it took six months of preparation to invade their country and insist that is the standard time. Measured from mid-July, when Polish labor unrest began, this would put mid-January as the start of the danger period.

Though Aspin did not say so publicly, it is known that one factor behind his analysis is the Soviet tendency to exercise its entire invasion force before using it. That process, some sources believe, is not yet completed.

The Soviets have more than two dozen divisions in six armies and on five different fronts surrounding Poland. The Russians have exercised each division and each army, including visits to each of those major commands by the overall Soviet commander. This was finished early in December. Many specialists here believed this was all that was needed.

But in the case of Czechoslovakia, the Soviets reportedly also had coordinated exercises of entire fronts as an entity before attacking. Since early December, and the initial public U.S. warnings, the Soviets reportedly have begun exercising these entire fronts and are nearing completion of these various communications and readiness tests.

Similarly, there are signs of other Soviet activities that appear to some to be more fundamentally preparatory rather than simply to "brush up" a force already set to move. This new activity reportedly includes assigning some Soviet personnel to Polish army units.

Aspin argues that an invasion after March would be tough because spring mud would bog down tank forces and also because of the peculiar Soviet style of mobilization.

Soviet reservists called up for mobilization are due to return home in March. The tour of duty for the last biannual call-up of draftees is due to end in May. Aspin believes that keeping both on duty would run considerable risk of disrupting the Soviet home front, economy and administrative apparatus.

The main evidence for lack of political preparedness, he says, is absence of a constant Kremlin propaganda line telling the world how bad things are in Poland. He also puts heavy emphasis on the attendance of Rumanian leaders at the Warsaw Pact summit meeting in Moscow on Dec. 6. Aspin says the Rumanians, frequently opponents of Moscow's foreign policy, would not have gone to such a meeting if they were convinced a decision to intervene had already been made.

Aspin's analysis differs most with that of the State Department, which, while not backing away from warning of the threat of invasion, tends to see the recent calm in Poland as a hopeful sign. The Central Intelligence Agency and the Defense Intelligence Agency also were among those that said Moscow was ready to move early in December if it wanted to. But those agencies have been less willing to suggest that the danger may be receding. Some sources suggest that Aspin's view is supported mostly within the supersecret National Security Agency, which monitors worldwide communications.