The Reagan administration, insisting that it would not have negotiated with Iran for release of the American hostages, yesterday put its formal stamp of approval on the agreement negotiated by the Carter administration and said it will implement details of the agreement.

At the end of a statement announcing the administration's intention to honor the agreement that led to release of the 52 American hostages, State Department spokesman William Dyess warned that President Reagan's approval of the deal should not be viewed as establishing a precedent.

"The present administration would not have negotiated with Iran for the release of the hostages," Dyess said. "Future acts of state-sponsored terrorism against the U.S. will meet swift and sure punishment."

Under questioning, however, Dyess refused to say exactly what the Reagan administration would have done in the Iran hostage situation. He would not go beyond the prepared statement's threat of "swift and sure punishment" in future cases.

The State Department announcement followed a four-week review of the hostage agreement reached in the final hours of former president Carter's term.

The agreement calls for freezing any assets found in the United States of the late shah Mohammad Reza Pahlavi and his family and fighting several hundred lawsuits by American claimants seeking payments from Iran and transfer of about $4 billion in frozen Iranian assets. Some of those assets would go to Iran, and some would go to Iran, and some would go into an escrow account for repayment of American claims as decided by a special commission.

The United States and Iran are to appoint members to the claims commission, a step that can now go forward. But as a practical matter, no additional Iranian funds are expected to be transferred to Iran or the escrow account until a Supreme Court decision on the legality of the hostage agreement.

Several American frims are challenging the legality of the agreement and Carter's power to agree to it. Reagan administration officials said yesterday that they are confident of winning a Supreme Court test on those questions before the end of the court's term this summer.

In announcing that it would implement the agreement, the administration stressed the legal arguments as it clearly tried to maintain some political distance between itself and a deal worked out by its predecessor administration.

"We are confronted with an accomplished fact," Dyess said. "We have an agreement signed by a president of the U.S., and the question is whether, given the existence of the agreement and the consequences (legal, financial and political) of implementing it or not, what should this country do?"

Asserting that reaching the agreement with Iran "was a legal exercise of presidential authority." Dyess said decision to honor the agreement "represents a practical judgment that implementation provides the surest resolution of the issue consistent with the best interests of the United States in the (Persian) Gulf region and throughout the world."

Administration officials noted that the decision to honor the hostage agreement did not change the overall state of U.S.-Iran relations and that any more toward more normal relations would be "very slow" to come about.

Earlier yesterday, lawyers representing several American firms with millions of dollars in claims against Iran raised several questions and concerns about the mechanisms to settle claims as set out in the hostage agreement. However, in testimony before the Senate Foreign Relations Committee, most of the lawyers suggested they could accept terms of the agreement if it is implemented properly.

Lawrence W. Newman, representing 37 law firms with clients seeking about $1.3 billion in claims from Iran, said his main concern is that Iran will not replenish the $1 billion escrow account to pay off claim awards as funds are paid out and the account's balance dwindles.

Newman urged the government to use the next several months to test Iran's good faith on a number or related matters, including the speed with which it appoints its members to the international claims commission, before surrendering control of any more Iranian assets in this country.

If Iran's attitude in the next few months is not cooperative, Newman said, "then serious thought should be given as to whether the remaining Iranian assets should be turned over. For under those circumstances, there will be good reason to conclude that Iran will fail to honor its crucial commitment to replenish the security fund."

Newman and other witnesses also urged that Iran be pressed to allow an expansion of the nine-member commission so claims can be processed more rapidly. CAPTION: Lawrence Newman, representing 37 law firms seeking about $1.3 billion in claims from Iran, and others testifying before Senate Foreign Relations Committee. By James K. W. Atherton -- The Washington Post