The growing economic warfare between the United States and Iran has escalated their 11-day-old crisis to a new stage that may bring serious negotiations as well as a further increase in international tension.

President Carter's action in freezing Iranian official assets was justifield as a direct, speedy and inevitable response to Tehran's move to withdraw its funds from U.S. banks.

Beyond this carefully limited public justificiation, however, yesterday's action can also be seen as the third U.S. step since Saturday to demonstrate both to Tehran and to the American public that the administration is not powerless to act.

The first step was Saturday's announcement of the crackdown on Iranian students in this country illegally. The second step was the cessation of U.S. oil purchases from Iran, announced Monday.

The freezing of Iranian assets, the third step, had been under consideration in the top ranks of the Carter administration since late last week, according to informed officials. The Iranian move to withdraw bank funds was considered a possibility even then.

Additional steps in this continuum ofmeasured action are not ruled out. While there is no sign that a preset schedule has been approved, well-placed sources anticipate a new American action every two or three days to maintain the pressure on Iran and to give outlet to the demand from the U.S. public for even stronger words and deeds.

In both countries, the danger is that a cycle of steps and countersteps will feed the already high level of public emotion rather than to keep it in check. This is one reason why the Carter administration has been extremely restrained in the description as well as the substance of the moves it has taken so far.

Along with the headlined contest of largely symbolic political and economic maneuver, two other major fronts are active in less prominent but probably more important fashion.

One is the continuing U.S. drive for negotiations, as direct as possible and at as high a level as possible, to obtain the release of the American hostages. State Department officials continue to expect that a channel for such discussions will open soon, apparently on the basis of hints in diplomatic channels that this is coming.

Iran's acting ambassador in Washington, Ali A. Agah, was expected to return from a quick trip to Tehran late last night bringing some word on the attitude and expectations in his home capital. Other indications are expected from the U.S. acting ambassador in Tehran, L. Bruce Laingen, who continues to be in daily contact with Iranian foreign ministry officials.

The U.S. resolve that Iran must release the hostages in order to obtain discussion of its desires and demands, stated very strongly at the State Department yesterday, is part of the positioning by the United States for the talks expected to take place.

By changing its formulation in the past several days of what is required from the United States, Tehran may also be engaging in positioning for further talks. Even though the new formulations have been judged clearly unacceptable, the State Department continues to see the shifts in position as a hopeful sign.

Although Ayatollah Ruhollah Khomeini rejected a visit from an official U.S. envoy, Ramsey Clark, the Iranian leader is reported to have agreed to be interviewed by Robert MacNeil of Public Television's MacNeil-Lehrer Report. McNeil is on his way to Iran.

Khomeini's apparent decision to take his case to American television may reflect some softening of his hard anti-American position, or it may reflect simply a bid for public support of his unyielding stance.

The other area of U.S. diplomatic concentration is a behind-the-scenes quest for the continued backing among third countries -- East and West, North and South -- for the demand that the hostages be released.

A widespread and sustained diplomatic drive since the early days of the embassy takeover appears to have yielded a broad international consensus on this point, but with unknown effect on the temporal and religious authorities in Iran.

As the struggle cotinues to expand in the economic area, the active or passive cooperation of European countries, Japan and the leading oil-producing nations of the Middle East becomes increasingly important.

With this in mind, the adminstration has kept in close touch with major foreign capitals through letters from President Carter to his counterparts and courtesy pre-notification, in several cases, of U.S. actions.

U.S. allies in Europe and Japan are much more dependent than the United States on imported oil, and thus are highly sensitive to a conflict with one of the world's major oil-producing countries. The other oil-producers also have a major economic stake in any such conflict.

Despite the large potential for seeking advantage at the expense of the United States, the key countries of the world appear to be solidly in Washington's camp.

This may be primarily because Iran's seizure of embassy hostages is outside the pale of acceptable behavior, rather than due to concern about relations with Washington.

When the hostage issue is resolved, the international solidarity may erode and a jockeying for oil and advantage begin. That remains in the middle distance, however, as the Washington Tehran tension continues to mount.