Administration officials said yesterday they still have not decided whether to prosecute former attorney general Ramsey Clark for defying a presidential ban on travel to Iran by participating in a conference there on "U.S. crimes."

State Department spokesman Tom Reston, responding to a published report that Clark and nine other Americans who attended the Tehran conference would be detained on their return, said the question of legal action was still under consideration and added:

"The administrationwill uphold the law, but there is also a concept in the law called prosecutorial discretion. The government will look at this as a legal question, and when a decision is made, an announcement will be made. The Department of Justice is the main agency, and the decision will come from there."

Officials of the U.s. Customs Service also denied a report published yesterday by the New York Dailey News that Clark's passport will be seized and that he might be detained when he arrives in New York. He tentatively is expected there today or Sunday.

Customs Service sources said an effort probably will be amde to ascertain from Clark whether he had been in Iran, in order to create an official record of his recent whereabouts in case legal action is pursued. But, the sources insisted, there are no plans to arrest Clark or the others, to detain them for detailed questioning or to take away their passports.

Clark, an outspoken critic of past U.S. policy toward Iran, took part in the Tehran conference as part of his effort to help free the 53 American hostages there. However, in doing so, he went against President Carter's order, issued in April, that invoked certain Treasury Department regulations to prohibit Americans from traveling to Iran or spending money there.

In attempting to come to grips with the situation, administration officials have been squeezed by a number of conflicting diplomatic, legal and political considerations.

On one hand, administration sources said, it must not appear that the president's order can be violated with impunity. That, they noted, would work against Clark's campaign to isolate Iran through economic and diplomatic pressures and could expose the administration to charges that it is too weak and indecisive to enforce its orders.

Possible trouble on that score was signaled yesterday by Sen. Robert Dole (R-Kans.), who introduced a Senate resolution calling on Carter to enforce the Logan Act, which bars unauthorized Americans from dealing with a foreign government in relation to disputes with the United States or "defeat the measures of the United States."

Calling the actions of Clark and the others "a flagrant breach of loyalty," Dole said they had aided Iran's hostility toward the United States "by condemning and insulting their own country."

However, administration officials noted that prosecuting Clark could produce a number of undesirable diplomatic effects such as helping to publicize the anti-American sentiments expressed at the Tehran conference and possibly providing Iranian militants with a further excuse for refusing to free the hostages.

In addition, the officials conceded, legal opinions differ about whether the president actually has the authority to bar U.S. citizens from foreign travel under circumstances like those in the Clark case.

The American Civil Liberties Union already has charged that the "right to travel is constitutionally guranteed and should not be abridged except when we are formally at war." That argument, if pursued in the courts, could lead to lengthy litigation and appeals that some federal officials fear could greatly confuse and complicate the government's ability to regulate overseas travel by Americans.