Besides an estimated $3 billion to $4 billion tied up in litigation over corporate claims against the Iranian government, another $700 million is tied up in potential claims by Iran against U.S. companies that once did business there.

In question is money American companies feared Iranians might call under performance bonds or standby letters of credit negotiated during the regime of the former shah. While Iranian assets were frozen, the Treasury Department set up arrangements to bar transfers of such funds out of corporate accounts until disputes over their legitimacy could be resolved.

Last week the Treasury Department issued a statement assuring American companies that the money would continue to be protected under regulations issued to implement the hostage release and the claims settlement agreement with Iran.

No regulations have been issued yet. The Reagan administration has under review the executive orders signed by former president Carter to carry out the U.S.-Iran agreement. In the meantime, however, Treasury officials have begun drafting regulations.

Parties with an interest in the agreement, including attorneys representing companies that have claims against Iran, have met with Treasury officials to offer advice about how the regulations might be drafted.

"These regulations, among other things, will make clear that contested liabilities and assets need not be transferred under these orders and that none of the orders affects standby letters of credit, similar obligations and substitute blocked accounts," Treasury said last week.

During the former shah's reign, a frequent feature of contracts between American corporations and Iran were clauses providing for performance bonds (insurance against contracts not being completed) or standby letters of credit in the nature of bonds to cover any claims for taxes or advance payments that were not later justified.

The clauses were written in a manner that allowed the Iranians to call the money "virtually at will," said former assistant Treasury secretary Rich Davis. Companies were concerned that the money might be called for political reasons and transferred into Iranian accounts.

Even though those accounts initially were frozen, companies sought protection to keep the funds in their own accounts. Treasury issued regulations that required U.S. banks to give notice to corporations involved, in the event of a call on the funds, and allowed the companies to acquire a license to block the transfer.

Essentially, the licenses held the situation in status quo until any question about the legitimacy of the call could be resolved.

Some 50 to 100 companies sought licenses protecting an estimated $700 million, while others went to court to challenge calls.

One company, Continental Telephone Corp., went to court both in the United States and Europe over performance bonds issued through European banks. The company was not sure it would be covered by Treasury regulations and sought additional protection, a company official said. European courts granted the company the relief it sought, he said.

Continental had been constructing a telephone system in Tehran but terminated the contract because of nonpayment by the Iranians, the official said.