The Atlantic Council says very few members of the 15-nation North Atlantic Alliance have "done as much as they should" to strengthen their conventional military forces in the face of growing Soviet power.

The council said yesterday that "unless the United States and its allies act promptly to reverse the trend, elements in the Kremlin will be encouraged toward the kind of "dangerous political adverturism or military coercion" that it said marked Soviet foreign policy after World War II.

Council members include former top security and diplomatic officials of past administrations. It describes itself as a nonprofit organization to promote the security and economic well-being of nations around the Atlantic basin.

The council said a gain in Soviet-Warsaw Pact conventional strength in firepower, mobility and striking range "has overbalanced improvements in NATO defense measures" in recent years.

"Warsaw Pact countries already have the ability to mount a major offensive without reinforcement, and the disparity continues to widen," the council said.

Without an adequate conventional defense, NATO would be faced with the choice of using nuclear weapons at the outset of hostilities or withdrawing in the face of superior forces, it said.

The council report criticized NATO countries for delaying essential modernization, cutting terms of military service and stationing troop units and supplies too far away from potential war fronts.