Ronald Reagan today raised the potentially volatile hostage issue in the presidential campaign, declaring that he didn't "understand why 52 Americans have been held hostage for almost a year now."

Reagan's statement was carefully prepared, though it was not included in printed excepts of the speech distributed to reporters here. The Republican nominee did not say what he would do differently to win release of the Americans who have been held for 352 days in Iran.

Reagan has rarely referred to the hostages in his general election campaign against President Carter, and it was not immediately clear why he had chosen to bring up the issue now. But one Reagan aide said that the GOP, nominee would like to put the president on the defensive "where he belongs" on the war-peace issue that has been hurting Reagan.

"I've heard that Mr. Carter this morning assembled members of the press corps to tell them that Ronald Reagan did not understand," Reagan said at a rally here. "Well, you know, for once I agree with him -- he's hit it right on the nose. I don't understand why we have had inflation at the highest peacetime rates in history. . . . I don't understand why his answer to inflation was to put 2 million people out of work. I don't understand why mortgage rates are at 14 percent.

"I don't understand why our defenses have weakened, why American prestiage has fallen abroad, why Afghanistan is now occupied by the Soviet Union [and] why there is massive instability in the Persian Gulf region . . . And lastly, I don't understand why 52 Americans have been held hostage for almost a year now."

Reagan's statement came at the end of a day in which he carried his political peace offensive into the nation's border region. He brought along a galaxy of Republican stars, including former secretary of state Henry A. Kissinger, to buttress his new proposal for SALT III and to attack the policies of the Carter administration.

"The president is determined to have me start a nuclear war," Reagan told an airport rally in Cincinnati. "Well I'm just as determined that I'm not going to. The matter of fact is -- I think that his foreign policy, his vacillation, his weakness, his allowing our allies throughout the world to no longer trust us or depend on us and our adversaries to no longer respect us, there's far greater danger of that unwanted inadvertent war through that kind of a weak policy than there is by someone in there who believes that the first thing we should do is rebuild our defense capability to the point that this country can keep the peace."

In addition to Kissinger, Reagan was accompanied today by former secretary of state William Rogers, Elliot Richardson, who held a variety of Cabinet posts in the Nixon and Ford administrations, and Senate Minority Leader Howard H. Baker Jr. (R-Tenn.).

All of them dutifully endorsed the proposal which Reagan made on national television Sunday night for a SALT III limiting strategic nuclear arms. All of them also criticized as unrealistic Carter's statement that he would take the rejected SALT II pact back to the Senate for a new try at ratification immediately after the election.

Kissinger called this move "a grandstand play" by the president. Baker said that SALT II would again be rejected by the Senate.

"Unless the Soviet Union agrees to restrain its international conduct, no arms control negotiation is going to succeed," Kissinger said.

When Kissinger was asked what he thought the Soviet response would be to Reagan's SALT III proposal, he replied: "They'll reject it with indignation from candidate Reagan and they'll accept it from President Reagan."

Kissinger went on to say that he thought Reagan's proposal for a SALT III without SALT II was workable but that it might be necessary to have an interim agreement between the United States and the Soviet Union that would incorporate the noncontroversial provisions of SALT II. His agreement with the GOP nominee's proposal was not surprising, since Kissinger was one of the architects of the speech.

Kissinger also spoke of the United States achieving "equivalence" with the Soviets in nuclear arms. In the GOP primaries, Reagan repeatedly said that U.S. "superiority" was what was needed. Asked about this, Reagan foreign policy adviser Richard V. Allen said that Reagan accepted the idea of "meaningful equivalence" in strategic arms but added that U.S "superiority" was desirable in other instances. He mentioned naval superiority as an example of an area where the United States should have more than equivalency with the Soviet Union.