President Reagan's choice to head strategic arms negotiations with the Soviet Union said yesterday any new agreements should require "equal overall limits" on both sides' nuclear striking power and at "a substantially lower level" than that allowed by the unratified SALT II treaty negotiated by the Carter administration.

Retired Army Lt. Gen. Edward L. Rowny told a Senate Foreign Relations subcommittee that a good place to start looking for such cutbacks is with the 308 huge Soviet SS 18 missiles, which dwarf anything in the U.S. arsenal.

In an opening statement and under questioning, Rowny essentially confirmed that when the administration proposes new arms talks, it will advocate big cuts in the kinds of weapons that most threaten the security of the U.S. retaliatory force.

Included are weapons with so much lifting power that each can carry perhaps dozens of individual atomic bombs.

The paradox is such a proposal is its similarity to that put forword early in the Carter administration, in March 1977. That proposal was flatly and quickly rejected by Soviet leaders, who viewed it as a betrayal of more limited reductions previously negotiated with the Ford administration.

Rowny, who represented the Joint Chiefs of Staff on the SALT negotiating team for six years, argued yesterday that the Carter proposal was "a good one" that would have reduced the threat posed by the biggest Soviet missiles and cut way back on other missiles and multiple warheads.

The problems, he said, was that the Carter administration "didn't have the will power to stick by it" in the face of the sharp Soviet rejection. Rowny maintained that the proposal was negotiable, tha the United States should have pressed for it and that failure to do so was one of the "disappoints" about U.S. policy that led to his retirement from the Army and his criticism of the agreements eventually negotiated.

Though the United States still has a sizable lead over the Soviets in numbers of individual warheads on land- and submarine-based missiles and bombers, Rowny said he "would be happy to trade" that lead if the Soviets would agree to reduce the throw-weight, or lifting power, in their land-based missiles force.

Rowny pointed out that the SS18 force has 1 1/2 times as much lifting power as the entire U.S. land-based force of 1,053 missiles, at least theoretically allowing, Moscow three times as many warheads.

Much of the U.S. numerical lead in warheads comes from submarine missiles regarded as less accurate than those fired from land.

Under questioning, Rowny made the administration's most specific public claim, saying that "we now have a condition of Soviet strategic superiority" in the nuclear field.

He said all estimates he has seen by the joint chiefs and secretary of defense say that sometime between the last quarter of 1980 and the first quarter of this year "the Soviets did surpass us in overall strategic superiority."

Rowny said limiting the throwweight and overall destructive power of Soviet missiles, not just the number of "launchers" that was limited in SALT I an II, is essential to prevent a rapid expansion of the Soviet missile force.

Rowny echoed the administration view that the United States first must build up it forces to get Moscow's attention. He said the United States would seek not superiority but parity in which each side undoubtedly would be improved in certain areas.

Rowny argued that the Soviets want and need arms control and "hopefully will see the folly" of a new arms race against superior U.S. industry, technology and economy.

But, he said, "there are only two ways to get an equitable treaty. Either the Soviets come down on their own violation, and I've seen very little evidence of that, or we go up to convince them that they have to come down."

Sen. Claiborne Pell (D-R.I.) said that sounded to him like a prescription for an arms race rather than arms control. Because of his background and the fact that he opposes past SALT processes, Rowny has been viewed with suspicion by many Democrats and some Republicans, including Foreign Relations Committee chairman Charles H. Percy (Ill).

The Council for a Liveable World, which opposes Rowny's nomination, claims the general's record "betrays more of an interest in promoting military weapons than in arms limitations and reductions."

Rowny repeatedly sought to "assure" the committee yesterday that he is "committed to genuine arms control," the kind, he said, that is consistent with U.S. security requirements.

He said that he will move quickly to get his staff in place and that, if he receives instructions to begin negotiations, "you'll find no hindrance or stumbling block in me."

Sen. Larry Pressler (R-S.D.) said the combination of Romny and his boss, Eugene V. Rostow, director of the Arms Control and Disarmament Agency, would be trusted by a large political body that otherwise might be suspicious of arms controllers.

Rowny said that the United States and the Soviets continue to abide by the SALT II agreement, even though it is unratified and not legally binding, and that he is prepared to continue that procedure as long as the Soviets do.

In SALT negotiations, Rowny claimed, the United States "possessed neither the leverage [in terms of new weapons projected] nor the negotiating skill" to obtain acceptable agreements.

By making arms control such a major part of foreign policy, past administrations, he claimed, "showed too much zeal" for agreements that the Soviets took advantage of. The United States, he claimed, failed to tighten loopholes and wording in the pacts, and this, he suggested, accounts for allegations of violations, a charge Rowny declined to make.

Rowny said verification of a new agreement will be far more difficult than in the past and will require cooperative verification rather than each side using only its own space satellites.