President Reagan's plans for deploying the MX missile, building a B1 bomber and otherwise strengthening U. S. strategic forces were shelled from all sides yesterday in the normally sympathetic Senate Armed Services Committee, in another important sign the controversial proposals may not survive intact in Congress.

Sen. Carl Levin (D-Mich.) dismissed Reagan's plan as "a shambles" that would leave the nation "worse off for the next five years than we are now."

Chairman John G. Tower (R-Tex.), while not going quite so far, said that the administration has yet to show the program "significantly improves the U.S. strategic posture vis a vis the Soviet Union."

Sen. Sam Nunn (D-Ga.) challenged Defense Secretary Caspar W. Weinberger, who was in the witness chair, to explain how the president's plan to enlarge existing silos to accommodate the big MX missile would not violate the arms control rules now informally in effect between the United States and the Soviet Union; Nunn plainly thought it would.

And Sen. J. James Exon (D-Neb.), who usually staunchly supports the Pentagon, told Weinberger, "I fail to see how I could in good conscience spend $20 billion to $30 billion" on the B1 bomber "if I were convinced" it could not penetrate Soviet defenses beyond 1990.

Weinberger seemed to flinch as he took one hit after another from the senators who have been assessing the president's strategic blueprint in 11 hearings. He shot back at Levin in one exchange, telling the senator his criticisms might lead people to believe the United States was still "the kind of weak and vacillating country it was under the previous administration."

Although partisanship did flare up during the strident hearing, both Republican and Democratic senators expressed deep doubts about the president's plans for deploying the MX in existing silos and building the B1 rather than waiting for the more advanced Stealth bomber.

Major parts of the president's strategic blueprint are in trouble in the House as well. The Appropriations subcommittee on defense already has voted against approving money for the MX and approved the B1 only by a two-vote margin in its first test last week.

Tower led off the contentious Senate hearing yesterday by reading a two-page statement complaining that the administration had raised "additional concerns while failing to allay some existing ones" in presenting the strategic program.

"Confusion within the executive branch," Tower said extends to how much the B1 bomber would cost, when it would be ready and how it would be used. The chairman added that the "effectiveness and purpose" of rebuilding silos to house the MX "are still unclear."

Then Tower called on Levin who read in a monotone the harshest indictment of the president's strategic package yet made by a senator:

"The administration's strategic program is a shambles. The proposed MX basing mode does not solve the Minuteman vulnerability questions that many perceive. It isn't mobile and simply makes bigger missiles more tempting targets . . . .

"As to the B1 bomber, the Department of Defense will apparently say just about anything to sell it . . . the cost of the B1 has been understated for no other apparent reason but to sell it . . . just a few weeks ago you told us that the Stealth bomber, which many of us prefer as an alternative to the B1, could be ready in 1989. Then the Department of Defense changed that to the early 90s with the obvious effect of strengthening the case for the B1."

Because some of the B52 bombers and existing Titan missiles will be retired earlier than the previous administration had planned, Levin continued, in strategic strength, "we will be worse off for the next five years than we are now. I've never heard of closing a window by opening it wider. This from an administration that promised to hit the ground running and to rearm America."

Weinberger replied that Levin had made "a great many misleading, dangerous, deceptive utterances."

The defense secretary said the administration is making a number of quick fixes to help redress the strategic balance, including putting MX missiles into existing silos until less vulnerable deployment schemes can be worked out.

The alternative to deploying the MX in silos as soon as possible would be "to leave it in the warehouses."

In exchanges with other senators, Weinberger said the B1 bomber, the first few of which are to be ready for duty in 1986, could not penetrate Soviet defenses after 1988 or 1989 "unless somebody wants to direct suicide missions."

Exon and Sen. Dan Quayle (R-Ind.) recoiled at the idea of spending $20 billion to $30 billion on the B1 when it would be good for only about four years as a manned penetrator.