The Carter administration insisted yesterday that a U.S. welcome mat is still out for the deposed shah of Iran, at least in principle.

In practice, however, officials said that Shah Mohammad Reza Pahlavi, now in the Bahamas, has been told repeatedly that it would be unwise for him to settle in the United States until a more stable regime has been established in Tehran.

This stance has been criticized strenously by Henry A. Kissinger, the former secretary of state, and David Rockefeller, chairman of the Chase Manhattan Bank. Kissinger saw his successor, Cyrus R. Shah's prompt admission.

Rockfeller, whose bank employs Kissinger as chairman of its International Advisory Committee, also has made several representations on the shah's behalf, both personally and through his staff.

However, administration officials firmly denied reports that either Rockefeller or Kissinger had been asked to explain the government's view to the exiled Iranian leader.

Instead, U.S. diplomats and at least one unidentified official outside the State Department have carried this message to the shah: If you come now, you could imperil the estimated 3,000 American still in Iran as well as your own life.

High officials here assert that there is no effective control in Tehran today over the police, the military and armed civilian bands.

If the shah, his family and entourage - a group of about 30 - took residence in exile here, it is argued, somre armed Iranian group might size Americans and hold them hostage in return for the former ruler.

In addition, officials said yesterday, there are hundreds of militant Irans living in the United States who have demonstrated their hostility to the shah and his former regime. They pose a continuing threat to his safety, it is argued.

Some aides also said that Iran's oil is a factor in the decision to urge patience on the shah. Although Tehran is selling its crude oil to nearly all comer, it is feared that granting asylum to the ex-ruler might lead to an order from the regime barring sales to U.S. refiners.

At the same time State Department officials indicated that some normalization of relations with Iran could be expected soon. Tehran and Washington intend to exchange ambassadors in the near future. Walter Cutler, currently U.S. ambassador to Zaire, has been reported as the likely replacement for Ambassador William Sullivan in Tehran.