The United States may not be able to make the next deadline set by the Iranian hostage release agreement: establishment, by Feb. 19, of an account in the Bank of England which over the next six months would receive $1 billion of now-frozen Iranian deposits held in American banks' domestic branches, sources inside and outside government warned yesterday.

This account would be used to pay off Americans whose claims against Iran would have been upheld by the international claims commission that is to be established under terms of the agreement.

The cause of the delay, sources agreed, would be the detailed legal review the Reagan administration is giving the complex multibillion-dollar deal, completed in the closing hours of the Carter Presidency.

Sources could not say yesterday exactly when the Reagan-ordered review would be completed. But they continued to emphasize administration statements that the agreement would be honored consistent with international and American law.

A further indication the Reagan review might push past the deadline is that the Justice Department has asked that legal action in the more than 300 claims cases against Iran in U.S. courts be delayed until Feb. 26. t

However, while the Reagan officials carry on their study of the Iranian hostage agreement, Americn bankers, with Treasury Department approval, were reported yesterday to be flying to London to begin discussion Monday with representatives of the Iranian Central Bank on distribution of a $1.4 billion escrow account controlled by Algeria.

That account was put together, immediately after release of the 52 American hostages, from previously frozen Iranian funds in overseas branches of U.S. banks. It was part of the $7.9 billion transferred to the Algerian account in the Bank of England from the United States under terms of the release agreement.

The bankers will attempt to arrange repayment of more than $1 billion in loans American banks had made to Iranian institutions during the regime of the late shah.And they will try to work out disputes between the Americans and the Iranian Central Bank on interest owed Tehran because of the freeze. a

Under the agreement, the United States, within 30 days of the Jan. 19 signing, was to establish with Iran a new escrow account in the Bank of England to hold the $1 billion earmarked for use in paying off American claimants.

At the same time, the U.S. government was to begin legal action necessary to release the $2.2 billion in frozen Iranian accounts in domestic branches of American banks that would be used in part to fill the proposed escrow account.

Government attorneys expect a legal challenge when they try to move those funds, and some expect that it will go to the Supreme Court.

Last week, officials said they doubted that the Reagan review would be completed in time to start these banking and legal actions by the agreement's 30-day deadline.

As part of the Reagan review, officials of the Treasury, State and Justice departments have been meeting with lawyers and other representatives of parties affected by the agreement, presenting ideas on how the implementation of the agreement might work -- ideas that are more favorable to American interests than originally expected.

The major provisions of the agreement call for:

Transfer of $2.2 billion of frozen Iranian deposits in American banks to the Federal Reserve Bank of New York for distribution at the direction of the treasury secretary. Of the first $2 billion, half is to go to Iran and the other half to the yet-to-be-established account for eventual payment to American claimants.

Transfer to the Federal Reserve Bank of additional Iranian financial holding, estimated at about $2 billion, now held frozen by American companies and individuals.

Transfer directly back to Iran of other frozen property, such as equipment, airplanes and works of art.

Prohibition of any hostages or their families from filing lawsuits against Iran for the taking of the embassy or the subsequent 14 months of captivity.

Establishment of regulations freezing the assets of the late shah and his family in the United States and requiring those who hold them to report their existence to the Treasury Department.

Opposition to the provisions has come from among the hundreds of nonbanking, corporate and individual claimants against Iran who are seeking more than $3 billion in U.S. court actions for property seized during the revolution or contracts with the former regime that were cancelled by the government of Ayatollah Ruhallah Khomeini.

In addition, Reagan officials have criticized the provisions that prohibited filing of suits against Iran by the former hostages and required American companies and citizens under threat of criminal action to report on assets of the late shah and his family.

The commercial claimants, under the hostage agreement, must bring claims before the new international claims body, which is to be established within nine months. In the interim, the parties involved are to attempt to resolve their financial differences directly.

At these informal off-the-record sessions with American claimants and their lawyers, government officials repeatedly say that the lawsuits in U.S. courts against Iran do not have to be dropped until the claimants are assured that the international claims group will take up their particular cases.

"If an American claim is not accepted by the group," one government lawyer said last week, "that claimant can proceed with his action in a U.S. court."