The Reagan administration stongly warned Americans yesterday against traveling to Iran, because the United States is unable to protect them from being arrested or taken hostage.

The warning, issued by the State Department, had the practical effect of replacing the ban on such travel imposed by President Carter last April 23 during the impasse over the American hostages.

That ban was lifted as part of the agreement freeing the Americans, and department officials said the new warning, while no prohibiting U.S. citizens from going to Iran, is intended to make them aware of the danger of such travel.

Department spokesman William Dyess said, "All U.S. citizens should avoid such travel because of the continuing anti-American feeling, the war between Iran and Iraq and the virulently anti-American stance of the Iranian government."

In the meantime, the Justice Department announced that it is asking U.S. federal courts to delay for 30 days acting on claims against Iranian assets in this country. Justice officials said the requested delay is to allow the new adminstration to finish studying the terms of the agreement under which the hostages were released.

As part of the agreement, concluded in the last hours of the Carter adminstration, the U.S. government is supposed to cancel claims by individuals and firms against Iranian assets frozen in this country and refer the claims to an international commission for settlement. Iran has said it will abide by the commission's decisions.

However, some of the more than 300 claimants have objected to this procedure, and have moved in the courts to nullify the part of the agreement that would take their claims out of American legal jurisdiction.

The Reagan administration has said it wants to study the details of the agreement carefully before going ahead with its implementation. On Monday, two of President Reagan's top White House aides -- presidential counselor Edwin Meese III and chief of staff James A. Baker III -- said the United States will honor the accord provided that the administration's lawyers are satisfied that it does not violate any provisions of American law.

The two, interviewed on public television's McNeil-Lehrer Report, stressed that Regan does not intend to repudiate the agreement, as some have suggested, on the grounds that the United States was forced to sign it "under duress." But, they added, before moving ahead the president wants to be certain that the agreement is fully legal and does not contain provisions "unfair" to any of the claimants or involved parties.

On Capitol Hill yesterday, Sens. Bob Dole (R-Kan.) and Dennis DeConcini (D-Ariz.) introduced a bill to permit American citizens and corporations to sue a foreign government in federal courts for compensation for injuries inflicted by the foreign government.

"The hostages and their families probably have no right under existing law to sue Iran in our courts," Dole said.

He said the bill would amend the Foreign Sovereign Immunities Act to eliminate a restriction that allows such suits only when the cause for action is committed in the United States.