The Joint Chiefs of Staff broke publicly with their commander-in-chief yesterday by declaring that President Carter's new defense budget is not big enough to meet the Soviet threat.

The chiefs were dragooned into the battle of the budget by Rep. Samuel S. Stratton (D-N.Y.), who called them before his House Armed Services investigation subcommittee to give their personal opinions on how much is enough for guns.

"Right now, we have a hollow Army," responded Gen. E. C. Meyer, Army chief of staff, in what turned out to be the bluntest response.

"I don't believe the current budget responds to the Army's needs for the 1980s," said Meyer of Carter's fiscal 1981 defense budget. "There's a tremendous shortfall in the ability to modernize quickly" in response to the Soviet threat.

Gen. Robert Barrow, commandant of the Marine Corps, when asked if the Carter defense budget was adequate, replied, "In a word, no."

Gen. Lew Allen Jr., Air Force chief of staff, said, "Increased defense spending is required to meet the increased danger."

Adm. James D. Watkins, deputy to Adm. Thomas B. Hayward, chief of naval operations, and speaking on his behalf, said Carter's fiscal 1981 defense budget "fell short of Navy requirements."

Watkins added that Hayward believes that if Carter's five-year program for the Navy is adhered to, "we would come close." He said, however, that Hayward was skeptical about the government sticking to that course.

Gen. David C. Jones, whom Carter has just reappointed to another two-year term as chairman of the Joint Chiefs of Staff, said that if he were a member of Congress, "I would not vote against the national defense part" of the compromise budget resolution now before Congress.

That resolution sets a ceiling of $153.7 billion for national defense spending for fiscal 1981. Carter opposes that ceiling as too high, asserting that it would "cheat the American people on domestic programs." His proposed ceiling is $150.5 billion, without counting adjustments coming from this week's pledge to increase military benefits.

Jones stressed, however, that the chiefs "have a narrow responsibility" which does not extend beyond defense to domestic programs competing for tax dollars.

Stratton said he wanted to find out from the chiefs where Carter received the advice that prompted him to oppose the national defense ceiling set in the budget resolution.

The subcommittee chairman added that he resented the letters Carter and Defense Secretary Harold Brown wrote to the Senate criticizing House additions to the defense budget.

Carter wrote Chairman John C. Stennis (D-Miss.) of the Senate Armed Services Committee on May 15 that the $6.2 billion the House added "could adversely affect today's military readiness by forcing offsetting reductions in the operations and personnel accounts. . . ."

Brown wrote Stennis on May 20 that the extra money would skew the balance of the federal budget and place "undue stress on our scarce economic resources and, ironically, jeopardizes the added military capability we all seek."

"I regard this as a very serious charge," said Stratton to the chiefs in zeroing in on those letters at the ouset of the hearing. "Where's the advice coming from?"

He asked the chiefs, one after the other, whether they had seen the Carter-Brown letters before they were sent to Stennis. Each answered that he had not.

The questioning then focused on whether the chiefs, in their personal opinion, believed Carter's proposed fiscal 1981 national defense budget is high enough.

None of the chiefs was asked to recommend a dollar total for the defense budget. Jones, who did most of the talking for the chiefs, said the United States was playing "catchup ball" with the Soviets militarily and therefore must increase its annual defense budgets indefinitely after allowing for inflation.

"We are interested in a longterm, real growth trend line," Jones said. He recommended raising the slice of the gross national product going to defense every year from the current 5 percent to "6 or 7 percent over the long term."

Under questioning, the chiefs said they did not subscribe to the complaint expressed in the Carter-Brown letters to Stennis that House additions to the president's fiscal 1981 procurement budget would end up jeopardizing military capability.

In elaborating on his characterization of today's Army as hollow, Meyer said U.S. forces in Europe are up to strength, but units in the United States are woefully short of combat soldiers.

To fill the gap, totaling about 20,000 soldiers, Meyer told the subcommittee, the nation is either "going to have to go to the draft or an adequately resourced all-volunteer force. Today we have neither."

The Army chief of staff complained that Congress in 1975 took away "the biggest incentive" for quality people to join the all-volunteer force, "the GI bill."

Marine Commandant Barrow, discussing the corps struggle to fill its ranks, said: "We are currently making the all-volunteer force work at great expense. We're hanging on the margin."

The coming drop in the nation's young population will make it more difficult than ever in the 1980s to find quality volunteers for the services, Barrow said.

The United States, he continued, does not want to find itself like "a car running out of fuel before it reaches the pump.The tank is running low."

Barrow predicted "a ranging debate" in the future over bringing back the draft. While not calling for conscription now, the commandant said the manpower problems piling up for the future lead him to believe that eventually "I would have to come down on the side of bringing back the draft."

Watkins said the Navy "simply must retain our career force," reminding the subcommittee that the fleet supply ship Canisteo could not put to sea for want of enough skilled sailors.

Pentagon studies, he continued, concluded that U.S. servicemen and women should be paid between $3 billion to $5 billion additional to make up for what they have lost to inflation in recent years. Carter's pledge this week to the Nimitz crew to increase military benefits by about $1 billion "is nothing more than a step in that direction," Watkins said.

The chiefs' testimony, in the Pentagon view, was an attempt by Stratton to drive a wedge between them and the president in hopes of swinging votes to the House resolution.

It is not unusual for military leaders to endorse higher defense budgets than the president is recommending when Congress demands their personal views. And Stratton insisted they appear before his subcommittee.

The timing, more than substance, is what gave the chiefs' dissent extra political thrust yesterday.

Pentagon spokesman Thomas B. Ross said yesterday of the chiefs' asking for more money: "This is not an unusual phenomenon."