From a variety of sources -- including a personal long-distance phone call into their splendid but spartan prison -- we have obtained a graphic picture of the conditions under which the three American officials trapped in the Iranian Foreign Ministry have been living for the past month.

The large room where the three embassy officials have been held since a radical student mob seized the U.S. Embassy in Tehran is furnished with Persian rugs, baronial coats of arms and tinkling crystal chandeliers. But the doors are chained shut and the three diplomats sleep on the floor, with only a sheet for cover against the chill night air of the Iranian capital. There is no heat, and for the first several days of their captivity, there was no water to wash in.

When water finally was carried in, the three men -- charge d'affaires L. Bruce Laingen, Victor Tomseth and security officer Michael Howland -- had to bathe in the same water. When they washed their soiled clothing, they hung it to dry on the chandeliers.

Unlike the hostages in the embassy, the three Foreign Service officers at the Foreign Ministry have had contact with the outside world. There is a working telephone in their room, and they have been allowed to make calls to their families in the United States. The calls are monitored, of course, and once Laingen was cut off abruptly in the middle of a conversation with his wife for no readily apparent reason.

The trio also has a television set, on which they are able to keep track of the situation outside their prison, or at least the situation as it is presented on the Iranian state TV station. Tomseth speaks Farsi fluently and is able to understand the speeches by the mullahs.

We asked Lee Roderick of Scripps League Newspapers, who accompanied Rep. George Hansen (R-Idaho) on his trip to Tehran, to check on the three hostages in the Foreign Ministry. He was the only reporter who got in to see them.

In an annex to the main Foreign Ministry building, Roderick was led down a corridor, up an elevator and along a winding passageway to a locked, chain-secured door. His escort gave a prearranged knock, and a guard peered at them through a peephole.

The door was opened, and Roderick was led through a kitchen and foyer into the large room where the three hostages were being held. Unlike the captives in the embassy, they were not bound or, apparently, forbidden to converse with each other.

Roderick told us that Laingen, a 57-year-old career diplomat and Middle Eastern expert who first served in Iran more than 25 years ago, appeared to be "strained, tense, nervous and disoriented."

Other sources said this was not from condern for his own situation or from discomfort at the primitive living conditions. Laingen spent a rugged boyhood on a Minnesota farm and has served in several hardship posts in nearly 30 years as a diplomat.

What was driving Laingen to distraction, our sources suggested, was the senior diplomat's concern for the hostages at the embassy and his anguish at being unable to be there to help them.

Students have descended on the Foreign Ministry several times and demanded that the three Americans be turned over to them. Iranian officials have put them off with reassurances that the three were being kept in custody.

Our sources slipped us the secret telephone number in their quarters, and we reached Tomseth. The conversation was unproductive in the sense of any hard news but was revealing of the circumstances under which the American diplomats were held and the professional self-control they were able to show after a month of harrowing uncertainty.

"We've heard that you three were being released, "I said. "We were delighted with the news. We wanted to find out how soon you'll be leaving."

"You know more about it than we do," replied Tomseth.

"You're supposed to be leaving about midnight."

"The wire services are carrying that, but we have no confirmation that the new foreign minister said anything to that effect."

"Nobody spoke to you yet at all?"

"That's right."

"How have conditions been there? . . . I'm sure you've been well treated. But is there anything you can say on the phone?"

"Our treatment here has been good. Ah, Mr. Anderson, because of the circumstances, I am sure you understand that I really can't tell you a great deal."

"Well, we look forward to seeing you when you get back, then. There's not much more that we ought to talk about now."

"No, I wish I could talk further, but given the circumstances I don't think I should."

"I understand. Look forward to seeing you when you get back."

"Okay."