Prominent Soviet dissident Yuri Orlov, whose arrest in February drew expressions of concern from the White House, has been formally charged with anti-Soviet activity, which carries a maximum prison term of three years, his wife reported today.

Irina Orlov emerged from a two-hour interrogation session with the KGB security police at Lubyanka prison to describe the nature of the charge against her husband.

She said interrogators had asked four questions about her husband, but she refused to answer any. She said in a statement that she considered her actions against her husband "immoral."

Yuri Orlov, 52, founded a dissident group last year to monitor Soviet compliance with the human rights guarantees of the Helsinki accords that the Kremlin signed in 1975. The monitoring group had issued about 20 reports on matters ranging from emigration and religious discrimination to the use of psychiatric hospitals to detain dissidents.

The official charge against Orlov is listed as "the dissemination of fabrications defaming the Soviet state." It was unknown until today how severly Soviet authorities would deal with Orlov. The scientist has been imprisoned since February, but his wife has not been able to obtain information about his case earlier.

After Orlov was arrested, the U.S. government expressed its concern directly to the Soviet embassy, rather than making a public statement as it had earlier when other dissidents were detained.

Since early spring, Soviet authorities have all but shattered the dissident Helsinki monitoring group, arresting nine members and allowing others to emigrate. One Western journalist, Robert Toth of the Los Angeles Times, was siezed and interrogated for several days earlier this month by KGB, ostensibly for receiving secrets from a Soviet specialist in parapsychology. In fact, KGB questioning centered on Toth's contacts with Anatoly Scharansky, a spokesman for the Helsinki monitoring group who was well known to Western Journalists.

Toth was compelled to signed a "protocol" regarding his contacts with Scharansky. He was finally allowed to leave the country after vigorous protests by the U.S. government.

Scharansky, 29, a computer specialist who had been refused permission to emigrate to Israel, was arrested March 15 after accusations in the Soviet press that he worked for the Central Intelligence Agency. His family had been told that he faces treason charges. The allegations were denied, by U.S. officials, including President Carter.

Soviet security officials are pressing the Scharansky case throughout the dissident community. Two Jewish activists were recently questioned about him and then granted exit visa to Israel that they had previously been denied. One of them was understood to have signed a "protocol" about the Scharansky case; the other reportedly refused to signed. It is thought that the protocols - a record of the interrogation session - may be used in the Scharansky trial.

The charge against Orlov is less serious than the charge lodged against Scharansky. It seems that the Soviets plan to separate Orlov's case from those of the other dissidein who have been arrested recently. Two members of the Helsinki monitoring chapter in the Ukraine are scheduled to go on trial Tuesday, but the charges against them have not been disclosed.

Another prominent member of the Moscow Helsinki group currently in custody is Alexander Ginzbur. No formal charges have been reported against him.

The handling of this case will be closely watched in Washington as a measure of Soviet reaction to President Carter's continuing outspoken stand on human rights. Moscow has denounced Carter's defense of dissidents as interference in this country's internal affairs.

Carter was reported to have told a group of newspaper editors in Washington over the weekend that Soviet anger over his human rights stand has proven a greater obstacle than he had previously believed to progress in the crucial strategic arms limitations talks.

The Soviet human rights record will be assesed at this fall's Belgrade conference to check compliance with the Helsinki accords, as will the performance of the other 34 signatories to the pact. The Kremlin has accused Orlov in the press of using his Helsinki monitoring group to discredit Moscow's positions at that conference.