The Joint Chiefs of Staff, in a report yesterday to Congress containing a gloomy assessment of the balance of power with the Soviet Union, said "a central question for the 1980s is whether Moscow will be more inclined to confront the United States in a developing crisis."

In attempting to answer that, the nation's highest-ranking military officers said "while the Soviets must still view a U.S.-Soviet conflict as extremely hazardous," Moscow now "may be more willing to accept the risks of confrontation, particularly where they have significant military and geostrategic advantages."

In a plug for President Reagan, who has just sent Congress a record $258 billion Pentagon budget authorization request, the chiefs said "the United States has begun to reassert the leadership necessary to restore confidence and consensus among its allies" after a period from 1971 to 1981 during which the Soviets spent 40 percent more on defense than the West did.

Even if the consensus to support increased defense spending continues, the chiefs said it will take four to five years just to "alleviate existing deficiencies." But the Soviet military advantage, the report said, "cannot be offset in a year or even a decade."

In their report on "United States Military Posture," the chiefs said that, despite Reagan's new $1.6 trillion, five-year defense plan, "truly effective" deterrence and defense require sizable commitments from allies in Western Europe, Japan and elsewhere to strengthen their forces.

The chiefs, venturing into foreign policy waters they usually avoid publicly, called attention in their report to current strains in the North Atlantic Treaty Organization and said that "despite the economic power of the European nations, some are failing to provide adequately" for defense.

In a global rundown of trouble spots and regional balances of power, the chiefs said that NATO's position in Western Europe "is improving" in the crucial central front facing the bulk of Soviet power but that the alliance's flanks in the north and south are in worse shape.

Spain's expected entry into the alliance is an eventual plus for the West, and the trouble in Poland makes clear that Moscow also has its hands full, the report indicated.

In the Caribbean, the report called attention to an aspect of the continuing confrontation with Cuba that is becoming a more prominent theme of administration policy. It said that 60 to 70 percent of U.S. oil shipping moves through the Gulf of Mexico and Caribbean and that Cuban or Soviet forces in the region pose a potential threat to allied reinforcement of Europe in a crisis.

The chiefs said a Soviet invasion of Iran is the "least likely" threat to U.S. interests in Southwest Asia but could also be the most damaging. While Moscow certainly would have the numerical advantage in comparison to a U.S. counterforce, the chiefs said, the Soviets would face severe problems moving troops and supplies through rugged terrain ripe for counterattacks.

Despite recent improvements in recruiting and retention of U.S. forces, the chiefs said, "the most critical concern with general purpose force readiness is the shortage of qualified military personel.

"Within Army units, the most pressing . . . problem remains the shortage of noncommissioned officers in combat arms, military intelligence and electronic warfare. The Navy is short of experienced petty officers" and others "requiring highly technical skills. All services are short of pilots," the report said.

In addition, the selective reserve that would reinforce active units in an emergency is 157,000 short of the peacetime requirement, although its strength has been growing recently.

As for the nation's strategic nuclear missile forces, the chiefs said their vulnerability today to Soviet missile attack "is the most serious problem."

The chiefs reported that "analyses project that a Soviet strike against U.S. missile fields could destroy a major portion of the land-based U.S. ICBM force if the U.S. chooses to ride out the attack before responding."

The Soviets, however, would still have to contend with the "secure and survivable" U.S. fleet of missile-firing submarines at sea and with bombers that manage to get off the ground before Soviet missiles land, the report noted.

In previous years, the chiefs' annual report has been presented as an "overview" by the JCS chairman. This year's report is identified only as being prepared by "the organization" of the joint chiefs and makes no mention of an overview or of the current chairman, Air Force General David C. Jones, who is scheduled to retire after four years in the job this summer.

A JCS spokesman had no immediate explanation for the change in form.