Bright yellow ribbons appeared on trees and railings in the U.S. Air Force hospital compound here tonight. A welcoming bedsheet banner, folded over to prevent premature disclosure of its message, hung from the balcony of the third floor where the 52 American hostages are expected to stay after finally being freed from Iran.

At the U.S. Rhein-Main Air Base opposite the busy Frankfurt airport 20 miles from here, huge banks of newly installed floodlights bathed the runway in a blinding glare. Cleared of snow by military bulldozers, the tarmac and the stands set up for as many as a thousand reporters and photographers remained eerily empty. The two C9 Nightingale hospital planes reserved for ferrying the hostages here were still parked in a dark corner of the airfield.

In a sudden flurry of activity following news of the signing of the agreement between the United States and Iran to free the hostages, final preparations were made today to receive them here for several days of rest, medical examination and debriefing before they go home. But then, as night fell and word came of another agonizing delay, the waiting game began again.

Slipping through the army of newsmen besieging the Air Force hospital, one of the first doctors to arrive here to examine the hostages said that physicians and nurses inside, their medical preparations completed, were anxiously listening to the final hours of the drama on radio "just like everyone else."

The top floor of the three-story main wing of the 235-bed hospital the largest American military hopsital in Europe, has been readied for the hostages.

The visiting government doctor said two hostages will be assigned to each double room. An Air Force spokesman described the rooms as typical for a military hospital, "government green metal beds and white sheets." Among the special arrangements, doctors said, is a telephone room from which the hostages can call family and friends anywhere in the world.

Medical officials said much of the hostages' first days here will be devoted to rest and medical testing. Their relatives have been strongly urged by the State Department to stay away.

Before meeting their families, the hostages will be counseled by doctors on psychological stresses they might experience. They will be shown television clips to bring them up to date on what has happened in the world during their more than 14 months of captivity.

The hospital, which was technically off-limits but physically open to journalists earlier during the months of waiting for the hostages' release, was completely sealed off today by heavily armed military police accompanied by guard dogs. Reporters are to be allowed onto the hospital grounds only briefly to witness the hostages' arrival there.

Tonight journalists and television equipment filled the sidewalks and streets around the hospital compound and climbed onto the fence-topped wall around it.