President Reagan was praised by his critics and assailed by his traditional champions yesterday for sticking with the unratified SALT II treaty.

Sen. Dale Bumpers (D-Ark.), for example -- a strong supporter of arms control -- called Reagan's decision "the most statesmanlike act of his presidency." Sen. Steve Symms (R-Idaho), a hard-line Republican, called it "unilateral disarmament and appeasement."

Bumpers and Symms represented the poles of opinion expressed in a wide range of interviews with lawmakers. The general assessment was that Reagan had electrified those who had begun to despair that no progress could be made on limiting nuclear weapons, had put the Soviets on the defensive at the Geneva arms talks and had left himself the option of breaking SALT II limits if progress there was not forthcoming.

Sen. John H. Chafee (R-R.I.), a supporter of SALT II adherence, literally pranced down a marbled corridor in the Capitol after hearing an administration briefing on Reagan's decision, telling reporters: "I feel great. I feel sensational. We've seized the high ground. The president's decision is good for the country, good for our allies, good in every respect."

Sen. Patrick J. Leahy (D-Vt.), who, like Chafee, has been critical of the administration's stance on arms control, seemed only slightly less ecstatic as he told a reporter: "I just called my wife to tell her that the president had a choice between arms control and an arms race and he chose arms control. I praise him for it, and our allies should praise him for it. His decision breathes new life into Geneva. Instead of being on the defensive, we can be on the offensive for a change."

Paul H. Nitze, the administration's special adviser on arms control, briefed senators on the president's SALT decision in a closed-door meeting in the upper reaches of the Capitol. He ran into some hostile questions, according to senators who attended.

"How are you going to get their attention," one unnamed senator asked Nitze in referring to the Soviets, "if you give in to them?"

Nitze responded to that and other critical questions, senators said, with the answer that "we want to go the full distance" on arms control while pressing the Soviets to comply with SALT II limits.

"I'm shocked to see the day when Ronald Reagan would be offering what appears to be unilateral disarmament," Symms told reporters.

Symms added that he felt a sense "of dismay" because the administration was "yielding to the whims of unilateral disarmament and appeasement, and there is no time in history that appeasement has brought peace in the world."

Sen. James A. McClure (R-Idaho), who has charged vociferously that the Soviets have shattered the worth of SALT II by violating its provisions, did not condemn the president's decision yesterday, noting that Reagan has left himself room to respond to any future Soviet violations.

Senate leaders and House and Senate lawmakers in key positions to oversee the president's military buildup issued strong endorsements of the SALT II decision.

Senate Majority Leader Robert J. Dole (R-Kan.) focused on Reagan's promise to make a "proportionate response" to any Soviet treaty violations, saying that this was a "clear message to Moscow" to adhere to SALT II or face a step-up in the U.S. strategic modernization program.

"Preeminently correct," said Senate Minority Leader Robert C. Byrd (D-W.Va.) of Reagan's decision. He added that he would rather dismantle Minuteman land missiles than scrap a Poseidon submarine to keep the United States from violating the SALT limit by 14 launchers when the Trident submarine Alaska goes to sea this fall.

Sen. Ted Stevens (R-Alaska), chairman of the Senate defense appropriations subcommittee, said, "I agree wholeheartedly" with the decision. He said Congress would "respond quickly" to any presidential requests for more defense money "tied to SALT II."

Sen. Sam Nunn (Ga.), ranking Democrat on the Senate Armed Services Committee, endorsed the decision but said he wanted to study the implications of scrapping Poseidon submarines to stay within the launcher limits of SALT II.

Rep. Les Aspin (D-Wis.), chairman of the House Armed Services Committee, said the decision "was unexpected but absolutely the right thing to do."