Iran's new president yesterday issued his harshest attack yet against the radical Moslems occupying the U.S. Embassy in Tehran, labeling them "self-centered children" after they engineered the arrest of a government minister accused of being a CIA ally.

In an interview with the Tehran daily newspaper Kayhan, President Abol Hassan Bani-Sadr denounced the embassy captors for behaving like "a government within a government" and said their practice of making unproven allegations against Iranian officials creates chaos.

Last night, the ruling Revolutionary Council, which appointed Bani-Sadr acting chairman Tuesday, backed his bitter protest against the militants by calling for the release of Information Minister Nasser Minachi, who was arrested early yesterday, according to reports from Tehran.

Since his election last month as Iran's first president, Bani-Sadr, who has called for a rapid solution of the embassy crisis, has been moving toward a showdown with the Islamic militants who have been holding an estimated 50 Americans hostage for 95 days.

U.S. officials, who see Bani-Sadr as the best hope for negotiating an end to the 13-week-old crisis, say the new president must first consolidate his own power and isolate the embassy militants who demand the return of Iran's deposed shah as the price of releasing the hostages.

Minachi, the first Cabinet minister to be denounced in a series of "revelations" by the militants, was arrested at his home at 2 a.m. yesterday after a spokesman for the captors said over national television that embassy documents show he was a collaborator of the U.S. Central Intelligence Agency.

One document cited was dated Dec. 8, 1978, a month before shah Mohammad Reza Pahlavi fled Iran, according to news reports from Tehran. The document allegedly said of Minachi: "He has been very thankful and frank with the embassy staff and has been passing information."

The minister was taken to Evin Prison where officials were reported be questioning him about his alleged CIA contacts. He was arrested on a warrant signed by an Islamic revolutionary court that apparently was prompted by the broadcast, observers said.

In an interview with Reuter after the broadcast, Minachi described the allegations as nonsense. He said the contents of the documents were "just the personal concept of the political officers of the embassy" whom he met before th shah was overthrown.

Bani-Sadr, who has consistently criticized the embassy takeover and is believed to have been responsible for Tuesday's departure from government service of the religious leader closest to the militants, stepped up his attack in the Kayhan interview yesterday.

"Why do they always put these children on the air without consulting the authorities?" he asked, combining his denunciation of the militants with another blast against the state broadcasting complex he claims has unfairly criticized him and other moderates.

Of the most recent broadcast, he said, "It is a self-centered action by the students. How can one rule a country when a group called 'students following the path of the imam' acts in a self-centered way and behaves like a government within a government?"

"It is the courts that must investigate those allegations," Bani-Sadr continued, "and the judge whether a person is guilty or not. Otherwise, chaos will be created in the country."

In a separate move possibly related to Bani-Sadr's growing power struggle with embassy militants, 50 Americans who were invited to Iran by the captors were delayed at Tehran's airport for four hours before being allowed into the nation's capital.

The militants are believed to have invited the American group, whose members are sympathetic to last February's revolution, to use them as a publicity vehicle showing that some U.S. residents are more interested in their grievances than the hostages.

Observers in Tehran say the radical youths may hope to discredit a "package deal" worked out by the United Nations that is being considered by Iranian authorities. It calls for holding an international inquiry into the shah's reign while the hostages are put in the hands of a third party.

A statement from the militants said the visitors agreed to avoid discussion of the hostages and to focus on Iran's revolution, according to news reports. The militants claim the hostages' troubles are small compared to Iran's past sufferings.

Before leaving for Iran, Norman Forer, the American group's leader, said in New York that there were no firm conditions for the visit. Forer, a University of Kansas faculty member who traveled to Iran in December, said the visit would last 10 days and he expected to "continue the dialogue. I hope I can caome back to say there were substantial changes."

The group consists of priests, lawyers, labor leaders, professors, blacks and Indians, according to news reports.