A team of more than 100 U.S. immigration investigators began moving into a federal prison here today to start their investigation of 171 Iranian men who face deportation for failing to disclose their identities.

The investigations, beginning this morning, could lead to deportation hearings as early as Monday against any of the Iranians that U.S. Immigration and Naturalization Service officials decide are in the country illegally, or violating the terms of their visas.

The Iranians, arrested after a demonstration erupted into violence in Washington last Sunday, continued to refuse to answer any questions today, let alone identify themselves to prison authorities.

But in contrast to the defiant, chanting group that was transported from the D.C. jail and sent here overnight, officials at the medium-security prison here described the Iranians as tired and "very docile."

"When you don't have an audience why act up?" William Patrick, associate warden of the prison, remarked about the demonstrators.

Prison officials said the Iranians are still refusing to eat any solid food, and will drink only some sugar and water after sunset, going beyond the terms of Ramadan, a Moslem month of daytime fasting. One Iranian, reported suffering from dehydration, was taken from the prison this morning to a nearby hospital, where he is being treated in the intensive care unit.

That Iranian, who refused to give his name to hospital officials and is listed as "John Doe," was suffering from convulsions and seizures, apparently from dehydration. He was unconscious when he arrived at the Horton Memorial Hospital in Middletown.

Later, two other Iranians were taken to the hospital, also suffering from dehydration.

Stanley Costello, the INS deportation officer now on the scene setting up for the massive investigation Sunday, said INS wants this matter settled "as quickly as possible."

"We're not going out of our way to deport any Iranian who is in (compliance with his visa)," Costello said. "If they can prove that they're here in status, they'll be released."

INS officials had originally said that anyone's refusal to give his or her name to authorities could well constitute grounds for deportation hearings. Costello said today, however, that any of the Iranians who can give their name and prove they are in this country on valid visas, "can walk right out of the door."

In Washington, acting INS commissioner David Crosland said only one of the 192 Iranians arrested last Sunday, including 20 women held in New York City, has cooperated with INS agents. He said the woman, who is being held in the New York's Metropolitan Correctional Center, gave her name and other information to officials. However, as of late today, INS officials have not been able to determine if she in the U.S. legally.

A second woman told INS agents that she understands and speaks only Farsi, the Iranian language, he said. An interpreter is being provided to assist INS agents in interviewing the woman.

Crosland said all of the Iranians who refuse to provide the INS agents with their names and other pertinent information will be presented official notice of deportation proceedings by Monday.

Under a seven-month-old INS regulation, all aliens must provide "full and truthful disclosure of all information requested" by agents or face deportation. That regulation was part of a Carter administration get-tough policy that followed the seizure of the American hostages in Tehran last Nov. 4.

Crosland said the decision to begin immediate deportation proceedings was coordinated with other governmant agencies, including the White House.

"This decision was not made in a vacuum," he said.

However, he refused to comment on what pressure, if any, came from the White House. A INS spokesman said the Iranians have been "a high priority" since President Carter's get-tough policy last fall.

He said the actual deportation could take as little a day or long as six to eight weeks.

If an immigration hearing judge orders any of the Iranians deported, they can appeal that decision to the Board of Immigration Appeals, which takes 10 days. The appeals board decision can be taken to the U.S. Court of Appeals, which generally takes another six months. However, Crosland said INS officials would initiate steps to speed up the appeal process.

Crosland said the Iranians are being advised of their right to legal counsel and that they will be offered three meals a day. "They can eat anytime they wish," he said. "They will be provided with sugar water if they refuse to eat."

He also said the Iranians will have access to doctors. "Anybody who needs intravenous feeding will be given it," he said.

The Iranians in Otisville are being housed in two separate unpainted cell-blocks, one to each 80-square-foot cell that has a window looking out onto the low-lying yellow brick buildings and the dirt and earthmoving equipment that are part of this unfinished facility.

The prison is not officially opened, and was chosen to house the male Iranians because it is one of the few federal facilities with adequate open bed space. There are currently 88 inmates here, but they are volunteers transferred from other prisons to help with painting and yard work to complete the prison.

The Iranians are being photographed, fingerprinted, and given complete medical examinations, as part of the routine processing required for all prisoners as they enter here.

Associate warden Patrick said that with the processing, especially the fingerprinting, "we will be able to identify most of them." If the Iranians entered the U.S. with legal visas, they were fingerprinted and photographed at that time.

The Iranians arrived at a nearby Air Force base at about 3 a.m. and were transported by five chartered buses to this secluded prison facility in the midst of the Catskill Mountains, 60 miles northwest of New York City.

They were offered breakfast at about 5:30 a.m. but none of them accepted. They were also served a regular noontime meal in their cells, but Patrick said all of them again refused to eat.

Meanwhile, Justice Department attorneys in Washington are still refusing any comment on a request by lawyers for the Iranian government for a full investigation of last Sunday's demonstration, and alleged police brutality, that led to the arrests.

The demonstration turned violent when protesters supporting the revolutionary government of Ayatollah Ruhollah Khomeini clashed with D.C. and U.S. park police during a simultaneous protest staged by anti-Khomeini demonstrators.

Most, if not all, of those arrested were Khomeini supporters.

Agence France-Presse reported from Tehran yesterday that Iran's permanent representative at the United Nations in New York has asked the U.N. for "speedy intercession" with the United States "to stop police violence against Iranian students." The Iran foreign ministry said the representative, Djamal Chemirani, told an assistant to U.N. Secretary General Kurt Waldheim that the arrest by U.S. authorities of demonstrating Iranian students earlier this week was "an illegal, savage act contrary to elementary human rights."

The U.N. official promised to relay the Iranian request to the secretary general, now on a tour of Southeast Asia.