"Walter, we're just minutes away from touchdown," intoned CBS correspondent Morton Dean to a mythical Walter Cronkite from a hotel room television studio on the eighth floor of the Sheraton at the busy commercial airport outside West Germany's business and financial center.

On another monitor is a cluttered makeshift control room across the corridor, correspondent Tom Fenton could be seen scanning the sky from the tarmac of the adjacent U.S. Air Force Rhein-Main Airbase for the C9 Nightingale medical evacuation plane that would bring the 52 American hostages here if they were released by Iran. "I think I see the first plane," Fenton reported.

On still another monitor amid the electronic equipment stacked to the ceiling in the cramped hotel room, a jet was followed smoothly by a battery of American television network pool cameras as it glided onto the runway, taxied and turned around. "They will be stepping out onto the ground here any moment now," Fenton said dramatically.

The plane was, of course, not one of the C9s ferrying the hostages from Iran or Algeria, but a regularly scheduled Lufthansa flight from somewhere in Europe whose passengers were unaware of the role it was playing in what could be the dress rehearsal by American television networks for one of their biggest live stories since the last moon landing.

For several hours this afternoon, the networks ran through the whole thing as though it were happening today -- from the round-robin, time-filling speculation among correspondents and studio anchors. On arrival, the hostages are to go by motorcade along high-speed autobahns from the air-field to the U.S. Air Force hospital in Wiesbaden, a resort and military town about 20 miles away.

Much of the information given viewers on the closed-circuit rehearsal had to be invented by the reporters, who animatedly described imaginary emotional scenes of uninvited relatives breaking through a cordon and mobbing the freed hostages before they could board ambulance buses for the ride to the hospital.

This and previous rehearsals, similar to recent run-through in Washington for Tuesday's inauguration of President-elect Ronald Reagan, have been especially necessary despite the long months the networks have spent on stakeout here and in Wiesbaden.

The sophisticated equipment, complex techniques, and satellite communications already have linked live coverage from Algiers, Frankfurt and Washington for newsspots beamed to the United States. The networks also must surmount tight restrictions on access here and what one executive producer called "bare bones" technical facilities despite the extraordinary buildup of expensive television resources.

In the Sheraton Hotel wing taken over by the networks, rooms are slept in some hours and used as broadcasting studios during others. Teletype and telex machines chatter away in bathrooms and clothes closets. Electronic equipment sits in sinks.

ABC has the most expensive and flashy setup. It's main hotel room studio, with maps and monitors on the walls, looks like it could be used to present the entire evening news every day. Its area of operation is the only one sealed off to the rest of the media and manned by public relations people from New York whose answers to queries are, "I'm afraid I'll have to give you a 'no' on that."

The key events -- the hostages' arrivals at the airport and at the hospital in Wiesbaden -- will be covered with pooled television pictures accompanied by individual "voice-over" commentary from anchors, correspondents and various experts here and in the United States.

In between this pooled coverage, the networks will rotate live reports from the various camera locations in strictly scheduled five-minute allocations of access time on the satellite relay. During this weekend's wait, longer segments of satellite time have been available for live reports on preparations here on the latest interpretations of U.S.-Iranian negotiations.

Satellite time is jealously guarded and occasionally argued over. Pool coverage responsibilities are strictly enforced. Competition to be first on the air with interviews and new scraps of information is expected by network officials to be intense.