Apparently reminding President Carter of his own deadline, the chief Iranian hostage negotiator said the U.S. government "has an opportunity only up to the end of office hours" Friday to take "a really practical step in connection with the transfer of Iranian's agreed deposits" to win freedom for the hostages.

In what could be interpreted as a threat of breaking off negotiations, chief negotiator Behzad Nabavi said "conditions will change dramatically" if nothing is done before the day is out.

"This is because the government of Iran has no wish to begin from scratch what it has accomplished toward this end during the past 70 days, and it holds Washington directly responsible for a lack of results from the measures already carried out," he added in an interview with the official Iranian news agency, Pars broadcast early today over Tehran radio.

Nabavi's words took on extra weight because he and Prime Minister Muhammand Ali Rajai yesterday visited Ayatollah Ruhaolla Khomeini, the patriarch of Iran's Islamic revolution whose seal of approval would be necessary for any decision to release the hostages or break off talks with the United States.

It was unclear from what Nabavi said whether he was talking of the Carter administration's deadline for agreement with Iran on terms for release of the hostages, or whether he was laying down Iran's own ultimatum. In any case, the message was that time has become a critical factor in negotiations apparently nearing a decisive point betwen Washington and Tehran through the Algerian government.

Also unclear was whether Nabavi was talking about office hours in Tehran or in Washington. Iran is 8 1/2 hours ahead of Eastern Standard Time, meaning 8 p.m. in Tehran would be only 11:30 a.m. in Washington.

Nabavi said that in his demand for practical steps to be taken he was referring to transfer to Algeria of assets not in dispute between the two countries. "Seventy days" was a reference to the complex negotiations conducted through Algerian intermediaies since Nov. 2, when the Iranian Majlis, or parliament, approved a set of conditions for ending the 14-month hostage drama.

His statement followed delivery to the United States of Iran's latest message on terms for the hostage's freedom.Diplomatic sources in Tehran had been convinced that the two sides were close to agreement. In Algiers, the relay point for messages between Tehran and Washington, diplomatics said Algerian officials also thought earlier this week that an accord had been worked out and were unsure what the final snags were.

Diplomatic sources here said that under the projected deal, Iran would get a little more than one-third of the $24 million in cash guarantees it demanded last month.

For his part, Nabavi said Iran accepted the "general principles" of an Algerian statement on the hostage terms -- in essence the last American proposals. But he gave no details of the "acceptance," under study in Washington, where it received Thursday afternoon from Algiers.

Instead, Nabavi seemed to emphasize his complaint that the U.S. government and American banks have dragged their feet in arranging for transfer of the Iranian funds. It was in this context that he spoke of a deadline by the end of office hours Friday, apparently meaning that the banks should begin arrangements for the transfer.

At the same time, he dismissed reports that the 52 hostages might be released at the same time the assets are transferred, saying:

"According to the statement of the Algerian government, acceptable to both sides, America has undertaken to deposit the Iranian assets . . . in the Central Bank of the third country before the release of the hostages."

Diplomatic sources in Tehran said the hostages would be released as soon as Algeria notified Iran that a certain amount has been deposited in the Algerian Central Bank.As soon as the plane carrying the hostages was out of Iranian airspace, Algeria would transfer the assets to Iranian control, they added.

Presumably because he was with Khomeini Thursday, Rajai did not receive ambassadors representing the European Community and Japan, who delivered a message to his office again calling for swift release of the hostages.

The note welcomed recent reported progress in the negotiations. It was delivered by the ambassadors of Denmark, France, Italy and the Netherlands. d

EC and Japanese envoys, joined by other ambassadors and charges including those of Sweden and Australia, also called on Ahmad Azizi, director of hostage affairs in the prime minister's office.

One ambassador said they had "a general discussion, including the hostages."

He said the envoys emerged from the meeting optimistic that the hostages would be released in a matter of days.