Navy leaders declared for the first time yesterday that the United States has lost its "narrow margin" of superiority over the Soviet Union, sliding into a "gray area" where neither side can be said to be ahead.

This testimony about the U.S.-Soviet naval balance was given to the Senate Armed Services Committee as Pentagon leaders were drafting requests to President Reagan to increase the inherited fiscal 1981 and 1982 defense budgets by as much as $30 billion.

The starting points for these additions are the record-time peacetime requests from former president Carter for $171.2 billion for fiscal 1981 and $196.4 billion for fiscal 1982. The new Reagan team at the Pentagon is proposing adding between $5 billion and $6 billion to the fiscal 1981 total and up to $25 billion atop the fiscal '82 request. If it is successful, the Pentagon budget will increase fully 25 percent this year to next.

Army, Navy Air Force and Marine leaders all seemed to sense that now is the moment to push for extra billions, with yesterday's testimony by the Navy the most outspoken yet.

"The budget before you is wholly inadequate," Adm. Thomas B. Hayward, chief of naval operations, told the committee. He complained it did not provide enough money for the ships and aircraft needed to restore maritime superiority over the Soviet Union.

"I cannot support the budget as submitted," Hayward said, "without amendments. And I cannot support its implicit acquiescence to maritime inferiority." Howard said that this time last year the Carter administration promised the Navy would receive money to buy 19 new ships in fiscal 1982. But, complained Hayward, the Navy got money for only 14 ships.

The admiral also called the Carter administration's procurement plan for Navy aircraft a "disaster." He said the 121 planes to be bought under the Carter budget are less than half the 330 needed to keep up with losses from accidents and old age.

Hayward said he called in fellow admirals last August to reassess the U.S.-Soviet naval balance and concluded he could not tell Congress in 1981, as he had in 1980, that the United States enjoyed "a slim margin of superiority over the Soviet Union." u

Continued Hayward: "One can't find that. I'm saying we are inferior. But I am saying that the gray area between superiority and inferiority is large enough today that it is ambiguous in terms of a professional assessment of who's ahead and who's behind.

"The trends of the last decade have led us to this point where even a slim margin of superiority has to be set aside. And that tells us what the commitment has to be in the decade ahead if we are going to restore ourselves to a position of maritime superiority."

Largely because the fiscal 1982 Navy budget earmarks so much money for such readiness accounts as spare parts and training, Hayward said, the procurement of ships and aircraft got short shrift. He complained that even counting the increases for readines, the Navy's budget grew only 1.6 percent, after allowing for inflation, between fiscal 1981 and 1982. This compares to a 5.3 percent real growth for the defense budget as a whole.

"For the first time in anyone's recollection," Hayward said, "the U.S. Navy is unable fully to meet its peacetime commitments" and would have to vacate "essential" areas of the world to respond to an emergency.

"Your country is overexposed and underinsured," Hayward told the committee. "Our margin of comfort is totally gone."

Navy Secretary John F. Lehman Jr. sounded a similar alarm, and then declared: "It must be clearly understood that our national security demands maritime superiority and nothing less."

Chairman John G. Tower (R-Tex.) termed the testimony of Hayward and Lehman "enormously disturbing." But Democratic senators Sam Nunn (Ga.) and John Stennis (Miss.) raised mild reservations during the open hearing.

Nunn questioned how the Navy could be portrayed as getting stronger all the time by Hayward and losing its margin of superiority over the Soviets in the process. He suggested to Hayward that before he reversed last year's assessment that the Navy would keep its superiority for the next five years he should have consulted Air Force leaders rather than just fellow admirals.

Stennis said that there was no doubt in his mind that the military services will get more money because "it's in the air." But the former chairman of the committee cautioned against trying to match Soviet forces in Europe man for man, declaring that former president Eisenhower had no such strategy in mind when he sold the committee on establishing the NATO alliance.

Stennis added that the U.S. military seems to be shouldering too much of the load for its allies. "What's our obligation to Japan?" Stennis asked. "What is it going to be in the future? We can't cover this whole globe. I think we've got to consider what we're going to do."

Commandant Robert H. Barrow of the Marine Corps joined the clamor for more funds as he sat with Hayward and Lehman at the committee witness table. He complained the marines are critically short of ships for transportion to distant trouble spots and are shooting up more ammunition in training than they are being allowed to buy.

Pleading for more "lift" ships for transporting Marine Corps is ready to fight in Camp Lejeune, N.C., and Camp Pendleton, Calif. That's not where the enemy is. Not yet at least."