A team of British lawyers from one of London's largest and best-known firms was credited today with having a crucial role in untangling the last-minute dispute that threatened to undermine the tenous agreement for a hostage release.

Members of the firm of Stephenson Harwood, which represents the Iranian Central Bank, overcame the final hitch by using open telephone lines to the Bank of England, the United States and Algeria in the desperate, around-the-clock negotiations that ended early this morning.

The firm, which has 33 partners and 280 staff members, has been representing the Iranian Central Bank since late 1979 in litigation here aimed at freeing Iranian assets frozen in London branches of U.S. banks, according to J. M. Fordham, a firm spokesman.

Fordham said the firm "deals with financial and commercial corporate work," not a surprising choice in the City of London, the term by which the financial heart of Britain is known. The City is also the center of much international finance.

In an interview Fordham gave some details of final negotiations. He said "several members of the firm were involved in around-the-clock negotiations over the last three days" with lawyers representing U.S. banks. But he said that "it does appear that our people found a way through to final agreement."

"Our work on the final legal and financial details of the agreement between the U.S. and Iran is just a natural extension of our work for the Markazi bank [the Iranian Central Bank] since the Iranian assets were frozen," Fordham said tonight.

Fordham refused to comment on what the final agreement entailed or what changes were necessary to secure it.

Tonight the firm released a statement on its involvement in the final negotiations; "Stephenson Harwood's involvement in these matters arose following the Carter freeze in 1979 because it acted for long established Iranian banking clients and it has been acting for Bank Markazi in relations to the legal issues arising since then. The Carter freeze caused serious, indeed, unprecedented, legal and banking problems for the City of London and international financial centers."

"The firm is very pleased that with the cooperation of the other advisers concerned, including several firms of City solicitors, the intensive work over the past days and nights has contributed to the settlement now reached."