Second thoughts on President Carter's cancellation of the B-1 bomber are producing serious questions on strategic policy, confronting the administration with problems for which solutions are not presently in sight.

A new debate over strategic policy seems ensured, now that the B-1 supersonic bomber - whatever its immense costs to the taxpayer - has been scrapped. Plans for such a debate are now being laid by defense-oriented members of Congress who want to know, among other things, whether Carter has hidden plans for some new and cheaper manned bomber to penetrate Soviet air defenses after the B-52 dies of old age in the next 10 to 12 years.

The deepening concern inside the defense bloc is that the virtual abandonment of the strategic (long-range) B-1 bomber - with no other replacement for the B-52 yet visible - was primarily a sudden money saving move with inadequate study of its profound implications.

Some of these implications seem, at least on the surface to pose horrendous new problems. For example, under the long-held American nuclear-balance thesis of mutual deterrence, the U.S. has allowed its air defenses to atrophy. The Soviet Union has done just the opposite.

No air defense has been developed against the low-flying cruise missile. Yet, even though U.S. experts hint broadly that the American missile may be equipped with electronic countermeasures that blind Soviet radars, the threat of an eventual effective Soviet defense against the cruise is real.

Moreover, it is axiomatic that what the U.S. does, the Soviets eventually can also do. Carter's decision to cancel the B-1 leading to all-out U.S. development and production of the cruise missile - not as an arms-talks bargaining counter but as the replacement for the long-range bomber - will predictably lead to a crash cruise-missile program in the Soviet Union. If successful, leading congressional defense experts warn, this Soviet capability will either force the U.S. into an immersely expensive air-defense program or hand the Soviets an unacceptable advantage.

"We've got the marbles right now with the cruise missile," a top military expert told us, "but 10 years down the road the cruise is going to turn into our problem, not theirs."

There is, moreover, growing suspision on another score on Capitol Hill, even among hawkish members of Congress who always have felt that the air launched cruise missile was the American ace in the hole. Without the B-1 to take a major role in the air-launched nuclear bomb force - one leg of the strategic triad - they fear the proposed 2,500-kilometer (1,550-mile) ceiling on the range of the air-launched cruise missile would be inadequate.

With the B-1 as its partner, it was felt that the cruise missile could be restricted to that maximum range from the point of launch. Without the B-1's versatility, that range will give sanctuary to vast Soviet areas, say congressional critics.

The effect of the B-1 decision on SALT hardly begins with the question of lifting that 2,500-kilometer range ceiling for the cruise missile. More important is the question of verifying the range, numbers and payloads of the Soviet cruise missile.

Verification lies at the heart of congressional worry about any new armscontrol agreement. Yet no way exists to verify the existenace of whatever numbers of cruise missiles the Soviets say they have - once they master development and move into production.

This presents the administration with a profound problem John L. McLucas, who as Undersecretary of the Air Force in the early Nixon days was head of National Reconnaissance - the top verification job - recently defined that problem.

In a letter to The Washington Post July 9, McLucas warned that "the President is moving away from a world of known weapon systems . . . to a world where there is no way to count how many each side has. He will have traded a temporary advantage in technology for a loosened control over weapons in general."

Underlying these rising concerns is the fact that Carter canceled the B-1 with no apparent offset of any kind from Moscow, a paradox deeply troubling to his critics.

The Presidents's new budget amendment asking Congress to kill $1.5 billion in B-1 funds and transfer $500 million of it to the cruise missile, was due on Capitol Hill this week. Carter is certain to get what he wants, but he may also get what he does not want: the start of a great debate on the strategic position of the U.S. as it looks ahead to a new period without the manned bomber.