The leading congressional champion of hard bargaining with the Kremlin, Sen. Henry M. Jackson (D-Wash.), praised President Carter's nuclear arms proposals yesterday, but questioned the wisdom of catching the Russians by surprise in public.

Jackson said the two nuclear proposals spurned by Soviet leader Leonid I. Brezhnev in Moscow last week were "eminently reasonable and sensible." In many respects, Jackson indicated, they paralleled his own recommendations to the President.

Jackson's remarks take on significance in view of the dispute in Washington over whether the United States miscalculated by presenting too hard a plan for Russian considering in Moscow last week.

Regarded as the pre-eminent congressional hard-liner on strategic arms matters, Jackson was a harsh critic of the negotiating policies of Henry A. Kissinger in the Nixon and Ford administrations.

Jackson told a breakfast meeting of reporters that "Carter has taken a gigantic step here of cutting back" on arms levels. "We're the guys in the white hats," Jackson said, and "I think we ougth . . . to keep our cool."

But Jackson, now being portrayed by Soviet commentators as the mastermind behind "tough" Carter administration strategy, said he thought the United States may have gone too far in pressing the Soviet Union in public with its new nuclear terms.

"Frankly," Jackson said. "I would not have gone public on this, but that is a matter of style, and [now] everything is 'in sunshine' . . . and this is a new experience for them [the Kremlin leaders]."

"You never want to push them into a corner [in public] . . . They are accustomed to negotiate under the rules of privacy."

Now, while the Soviet Union really ponders the implications of the American offer they initially scorned, Jackson said, "I don't think we should overreact at this point." Instead, he said, "It ought to be a measured response, sensible and restrained . . . not inflammatory." Jackson said, "I am convinced that the President is going to remain fundamentally firm."

The implications of no new overall nuclear arms accord, and no restraints whatever on the cruise missile, Jackson said, must be recognized by the Soviet leaders. The cruise missile, he noted, "raises all the nightmares of arms negotiation" as a new, "invulnerable item" that is "very cheap, relatively" to produce, and requires "a whole neew set of principles" to control.

Jackson said he had breakfast with President Carter (on Feb. 4) and then submitted to him (on Feb. 15) a 23-page memorandum of ideas for the recent nuclear arms control plan.

There are many parallels between the U.S. plan and Jackson's. Jackson, for example, proposed a limit of 1,760 on U.S.-Soviet nuclear missile launchers and intercontinental bombers the Carter administration figure in Moscow last week was 1,800 to 2,000.

Defense Department officials yesterday revealed more details of the cruise missile portion of the American negotiating offer in Moscow.

Under the Carter proposal, they said, the United States would limit its cruise missiles to a range of 2,500, kilometers, or 1,550 land miles.

In a report from Paris last week. The Washington Post reported that American sources said this cruise missile range limit was 2,500 miles, rather than 2,500 kilometers. That source incorrectly referred to miles rather than kilometers, Pentagon officials said yesterday.

In addition, defense officials said yesterday, only bombers regarded as strategic could be armed with cruise missiles with that much range. The American B-25 bomber is in this category, but no the Soviet "Backfire" bomber under the terms of the Carter proposal.

Short-range bombers, considered tactical aircraft, rather than strategic aircraft, could not carry cruise missiles with a range of more than 600 kilometers, or 373 miles. The Soviet Union, however, has sought to impose that 600-kilometer limit on all cruise missiles. This range limit would validate existing Soviet short-range cruise missiles, which lack the major technological advances of U.S. long-range versions.

Defense officials said an American cruise missile, which is similar to a jet-powered, pilotless plane, at a range of 1,550 miles would have less range that the combat radius of the Soviet Backfire bombers. That range, they said, is 2,000 to 3,000 miles, without resorting to refueling in the air.

Both these weapons, the American cruise missile and the Soviet Backfire, have been the core of controversy since 1974.The long-range cruise missiles, however, are by far the most potent new weapon.

The Carter proposal offered to count the Soviet Backfire bomber as a tactical, not a strategic, bomber, in a "comprehensive package" plan, if the Soviet Union would accept major reductions in existing total strategic nuclear forces.

Defense officials said yesterday, however, that they are waiting to hear from the Soviets what assurances they could give that the Backfire would not be used as an intercontinental, strategic weapon.