President Carter is weighing additional economic steps against Iran in the new few days but is not contemplating military action until after the mid-May "reassessment" of the efforts to free American hostages in Tehran, White House officials said yesterday.

There was specultion, which was not confirmed as of last evening, that Carter may announce the latest economic steps as early as today, when he was tentatively scheduled a news conference.

Presidential press secretary Jody Powell said any new steps would be "meaningful and constructive" rather than merely symbolic, and suggested that the measures were being designed with an eye toward maximizing support by U.S. allies in Europe and Japan.

On April 7, Carter went most of the way toward shutting down remaining U.S. commerce with Iran by imposing full-scale sanctions. Among the further steps reported to be under consideration now are banning all imports from Iran and prohibiting U.S. ships from carrying Iranian cargo.

There were some suggestions that an across-the-board embargo on U.S. trade with Iran is under study.

Powell denied a report in The Boston Globe that the United States is prepared to impose a naval blockade on Iran if nonmilitary measures fail to break the hostage stalemate by mid-May. Characterizing the report as "wrong," Powell said that, as of now, "President Carter has not decided on a blockade."

Administration officials have made clear in the last several days that they have set the middle of May as a deadline for a major U.S. reassessment of the Iran crisis.

Late last month, U.S. allies were informed that they might be asked to break off diplomatic relations with Iran by the middle of May if measures did not bring substantial progress toward release of the American hostages.

Secretary of State Cyrus R. Vance is planning to attend the celebration of the 25th anniversary of the Austrian peace treaty in Vienna May 15-16. Soviet Foreign Minister Andrei A. Gromyko is expected to attend the event on May 16, and there are indications that the top U.S. and Soviet diplomats will seize the occasion to discuss the growing strain between the superpowers regarding Iran and the continuing tension over Afghanistan.

Administration officials said, however, that Carter has not yet approved a wide-ranging Vance-Gromyko discussion in Vienna. If a top-level U.S.-Soviet meeting does occur, it will be the first since the taking of the American hostages by Iranian militants last Nov. 4 and the soviet invasion of Afghanistan Dec. 27.

Vance is also expected to discuss the Iranian situation with U.S. allies during his European trip, possibly in the form of a meeting of NATO foreign ministers.

U.S. sources gave some additional detials and assessments yesterday of the reports of a buildup of Soviet military forces in the Transcaucasian military district adjacent to the Soviet-Iran border. The reports, which have circulated in Washington since early this year, were given new prominence by a broadcast interview Monday night with presidential assistant Zbigniew Brzezinski.

Brzezinski's point in citing the reported Soviet activity was to warn Iran that it faces a serious threat from the north, which makes the continued U.S.-Iranian conflict over the hostages dangerous as well as pointless.

State Department spokesman Hodding Carter said the current U.S. analysis of the Soviet activity does not suggest that it is "aimed at the border of Iran."

Carter said the U.S. studies "see no intention" by the Soviets to move into Iran militarily, but he added that the "enchanced capability and level of activity" should be a source of concern to Iran.

Official sources said U.S. intelligence reports indicated a steady though gradual increase in the manning level and readiness of Soviet units in the Iranian border region beginning late last year. A U.S. analysis completed within the past week is said to have note improvements in Soviet air defenses, armored personnel carries and communications capability.

The communications improvements is reported to have attached special attention because the radios involved are not usually given to Sovien units on routine border duty.