President Reagan "is going to run into disaster" with his rearmament program unless he recognizes "the real world" of defense spending and helps Congress cut the Pentagon budget, Rep. Bill Chappell Jr. (D-Fla.) told Defense Secretary Caspar W. Weinberger yesterday.

Chappell, chairing the first hearing of the House Appropriations subcommittee on defense since the death of former chairman Joseph P. Addabbo (D-N.Y.), was joined by several other lawmakers in calling for administration help in breaking the congressional impasse on the defense budget.

Rep. John P. Murtha (D-Pa.) urged Weinberger to press Reagan to raise taxes as a way of saving an otherwise doomed defense buildup.

Weinberger was unbending at the witness table, declaring that he was not "authorized" to ask for any less than the $311.6 billion in Reagan's fiscal 1987 defense budget, $33.2 billion and 12 percent more than the current level.

Weinberger was supported by Adm. William J. Crowe Jr., chairman of the Joint Chiefs of Staff, who was sitting beside him. Crowe said the Soviet threat does not permit economizing on defense.

"We're at a critical juncture," Crowe said in warning against deep defense cuts. He said it would be "a grave error to allow the Soviets to widen the gap" in the U.S.-Soviet military balance by refusing to fund Reagan's defense buildup.

None of the committee members bewailing the administration's uncompromising position on its new defense budget mentioned disclosures made by David A. Stockman, former White House budget director, about how Reagan's rearmament program is much more costly than originally intended.

Discussing his book, "The Triumph of Politics," on PBS' "Frontline" Sunday, Stockman said he and others in the Reagan camp assumed that they would add 7 percent for defense atop a $142 billion budget to be inherited from former President Jimmy Carter.

However, Congress and Carter had raised that starting point to $222 billion by the time Reagan took office. The Reagan administration began with that total, even though it was $80 billion higher than contemplated, and projected annual increases of 7 percent more than that higher total between 1980 and 1986.

Because of the compounding effect, the actual annual increase of 10 percent was twice the 5 percent promised by Reagan during his 1980 campaign.

Besides assailing the administration for not cutting deeper into defense, several members of Congress are faulting reductions recommended in the pending fiscal 1987 budget.

Sen. Carl Levin (D-Mich.), for example, said last week at a Senate Armed Services preparedness subcommittee hearing that, by favoring the Strategic Defense Initiative and major procurement programs over purchases of ammunition and spare parts, "the administration has turned its back on readiness."

Levin faulted the Army and Navy for buying fewer munitions in fiscal 1987 than in the current year and the Air Force for skimping on spare parts for aircraft. If this is not changed, Levin said, "it will only be a few years before we have an Army which runs out of ammunition, an Air Force with grounded planes and a Navy with ships that can't go to sea."

Weinberger complained to the House panel yesterday that the Gramm-Rudman-Hollings antideficit legislation gives him no flexibility, starting in fiscal 1987, in deciding what to cut and what to spare but will require uniform cutting of accounts. CAPTION: Picture, Secretary Weinberger: not authorized to request less than $311.6 billion. The Washington Post