Even before the freed U.S. hostages touched American soil two days ago, many American companies received requests from Iran to resume "business as usual," administration sources said yesterday.

Iranian firms have sent telexes asking for a range of goods from animal feedstuffs to industrial gas turbines to safety valves for heating and plumbing, companies revealed yesterday. Many U.S. firms have contacted the Commerce Department and Treasury in the last week to find out whether they may now start trading again with Iran.

The speed with which Iranian firms have acted suggests that the trade embargo imposed last April has been biting. It also dramatizes the decision that President Reagan must make about whether to uphold the agreement with Iran signed by President Carter the day before he left office.

Technically this lifted the trade embargo, the Commerce Department said yesterday. But it has been cautioning firms that since the agreement is known to be under review by the new administration, it might be wise to wait for an official announcement before resuming trade.

Reagan has to decide whether to normalize business relations with Iran despite the political distaste he may feel over this, or whether to upset those firms who want to start making money on Iranian trade again. European countries and Japan lifted their trade sanctions against Iran last week. An announcement on U.S. policy is expected in the next week or two, according to some of the companies involved.

Several firms contacted yesterday said that they will not reply to Iranian requests, and will not start shipping any goods, without such an official go-ahead.

Others said it was "premature" to talk about resuming trade as long as other arrangements, chiefly the settlement of outstanding claims against Iran, were unresolved. Some 388 firms that had significant interests in Iran before the hostages were taken are now claiming about $3 billion, administration officials said yesterday.

Larger firms, such as E.I. du Pont in the chemical field, which did a lot of business with Iran but have lost money there, seem more concerned about reclaiming that than about starting to do business again. An administration official said that the claimant firms are more vocal than the would-be traders so far.

A spokesman for du Pont said yesterday the company had had no overtures from Iran and that it was "too soon to tell what our position would be" about trading again. Another person in the company said he could not imagine a resumption of trade after what had happened.

International Harvester, the largest truck manufacturer in the United States, said that the company had recently been asked to supply Iran with industrial gas turbines but that it was "not doing business with them at this time." The spokesman would not say whether this was for legal or other reasons, but added that it was "primarily an internal decision."

A spokesman for Raytheon Co. in Boston said it had not received any telegrams and had "no plans to resume trade with Iran in the foreseeable future."

On the other hand, Watts Regulator Corp., a medium-sized private company in Lawrence, Mass., would like to start supplying Iran again with the safety and control valves that it makes for heating and plumbing. Several Iranian firms have approached the company since last week, according to Paul Richie, export manager. He was anxious to have a final answer from the administration about the legality of trading again before losing the market to European and Japanese competitors.

And a spokesman for Croptex, a small private company in Chicago, said it would also like to start supplying Iran with animal feedstuffs once it is sure this is legal.

Westinghouse Electric Corp. got a telegram requesting supplies from one of its small motor divisions, Christopher C. Newton, a spokesman, said yesterday. "We're just waiting to see what the U.S. goverment's policy is, what American companies should do in this case," he went on.

Richie said his understanding was that the position was "kind of cloudy" although the embargo has been lifted. The agreement Carter signed on Jan. 19 included a lifting of the trade embargo, which was then published in the Federal Register on Jan. 23. Normally this would have the force of law.

It was thought last week that Treasury might have to issue regulations promulgating the ending of the ban, but this is now not expected, government sources said yesterday. However Treasury is not telling companies that it is all right to resume trading, but is merely repeating that the Carter agreement and executive directives were signed and published last week, and leaving it up to them to decide how to act.

Bill Wright, a spokesman for Electric Data Systems, said yesterday that the Dallas firm, which provided computer services in Iran, has not been contacted by the Iranians and does not expect to be. "Considering all the litigation going on it's very unlikaly that they would contact us," Wright said.