President Carter's new trade and financial sanctions against Iran are mainly symbolic and will not have any visible impact on the Iranian economy for several more months and possibly for years, officials said yesterday.

Rather, the moves seem intended both to assuage demands by American voters for tougher action against Iran and to make it easier for U.S. allies to impose similar sanctions of their own.

White House officials said yesterday the sanctions were hammered out with a view toward showing Iran what they might foreshadow," not because the actions involve any "overriding" amounts of trade or finances.

The question of how much impact yesterday's actions will have involves these elements:

Carter's order prohibiting American firms from exporting to Iran will involve only a few million dollars at most. The United States exported $1.6 million worth of goods to Iran in February, compared to $100 million a month under the shah.

The ban on American exports does not apply to food and medicine, but officials noted that in both cases current shipments to Iran are minimal. Thus, the exemption is not expected to mean much in practical terms.

Carter also ordered the Treasury to begin taking formal inventory of the $8 billion or so in frozen Iranian assets here, with plans to use the money to pay damage claims filed by American corporations and the families of hostages.

However, the process not only requires congressional approval of new legislation, but hearings and case-by-case decisions by the U.S. International Claims Settlement Commission -- a procedure that could take years.

The actions will not have any direct impact on the amount of oil the United States is able to import, according to officials. The United States stopped buying Iranian oil months ago and only a few lagging shipments remain on the books.

Iran still is selling oil to Japan and Western Europe -- a factor that has been a major sticking point in White House efforts to persuade the allies to go along with sanctions.

The United States tried earlier this year to get the United Nations Security Council to vote economic sanctions against Iran, but the proposal was vetoed by the Soviet Union after 10 members voted to support it.

Another key consideration in the administration's action yesterday is to what extent the president's proposed new procedure for claims against Iranian assets might be superseded by the courts.

There now are some $3 billion in claims pending before federal courts around the nation -- $2 billion from banks alone and the bulk of the remainder from U.S. corporations. At least one or two of these cases are close to a decision.

Treasury officials said yesterday they hoped the courts did "not move forward" on these cases until Congress has a chance to enact the new legislation the White House is proposing. But they conceded there is no way to block a decision.

The White House has not yet decided what specifically to ask for in any new legislation. Officials said yesterday the proposal involves complex legal issues, most of which still must be worked out.

Nevertheless, the procedure is expected to be more rapid than traditional U.S. claims-settlement efforts, some of which have continued for as long as 30 years. One difference this time is the United States already has Iran's assets on board.

Treasury sources said the claims plan was fashioned to include the families of American hostages partly in deference to Congress, which already is considering legislation to deal with family claims.

Officials said there is no question the $8 billion in assets the United States froze last autumn would be more than enough to handle any anticipated claims. There were suggestions that the hostages' case might be handled as a single claim.

There was no immediate indication whether major U.S. allies would go along with the administration's newest request that they join in with similar sanctions.

A Treasury Department order asks companies or persons who believe they have claims against Iran to report them by May 15. The actions would involve claims stemming from expropriations, nationalization or defaults on loans or salaries.

A Treasury official said yesterday the White House hoped that the new action would persuade the Iranian government that the sanctions now are "semi-permanent" and that any shortages Iran is experiencing "are going to get worse."

However, the United States appears ready to withdraw the sanctions if the situation involving the hostages changes.