Dubbed the "Freedom Express" by its weary passengers, the first American evacuation flight from Iran landed here today after a joyous flight that began only after eight tension-filled hours of intimidation by revolutionary militiamen at the Tehran Airport.

Boisterous cheering went up in the Pan American World Airways Boeing 707 jetliner as it lifted off the runway at Mehrabad Airport after the long passport checks, body searches and questioning at gunpoint of the 152 passengers.

More flights, chartered by the U.S. State Department, are scheduled for today to continue airlifting an estimated 5,000 or more Americans from Iran in an emergency evacuation plan. The U.S. Embassy in Tehran declared yesterday that it could no longer guarantee the protection of American citizens in Iran.

From 6 a.m. to 2 p.m., when the plane finally departed Mehrabad, the passengers -- including employes of Pan Am, the Tehran Intercontinental Hotel, defense contractors and some U.S. government ment officials in sensitive posts -- waited while guerrillas argued among themselves about departure procedures and combed the passengers looking for "subversives" who might be attempting to flee the country.

At the last moment, militiamen took into custody an Afghan passenger and temporarily held for questioning several Americans because they were suspected of smuggling out "documents vital to the revolution."

The Americans, including Tehran Intercontinental Hotel manager Gary Hoagland, were finally released and the plane was allowed to take off.

Among the passengers were 20 correspondents being rotated out of Iran after covering the revolution and the subsequent fighting between rival insurgent organizations.

Throughout the eight hours of waiting, the armed militia herded the passengers from one security check to another taking names, examining documents and baggage and conducting personal searches.

Several militiamen said the scrutiny was necessary to prevent the escape of "enemies of the revolution" and Afghans nationals. An estimated 3,000 Afghans, mostly laborers, have been rounded up in Terhan over the last several days and marched blindfold to makeshift detention facilities at the headquarters of revolutionary leader Ayatollah Ruhollah Khomeini.

Some Iranian wives of departing Americans also were subjected to persistent questioning and berating by militiamen, who seemed unable to agree on who would be allowed to leave and what security procedures should be followed.

An American businessman who attempted to photograph militamen guarding the passengers with automatic rifles had his film ripped from his camera. One militiaman attempted to take a Persian rug from a passenger, abusing him for taking the "people's property" from Iran.

As if to underline the conflicting attitude of the security officials and the constant bickering among them over procedure, one security official announced over the plane's loudspeaker just before departure: "These are not normal times and I hope you return when things get better."

The crew of the airliner, all of whom came to Iran voluntarily after standing by with their aircraft for a week in Bahrain, appeared nervous about the numbers of weapons carried by the rag-tag collection of militiamen.

"When we first saw all those dudes with those guns, we got on the floor and prayed," said Joyce Horton, a a Pan Am stewardess from Richmond, Va.

She said she volunteered for the flight "because I needed a little excitement, a new routine for parties."

In addition to the normal flight deck crew, the plane carried Pan Am's chief pilot and a backup pilot because of the risks in landing without normal navigation aides on the ground. Air traffic controllers in Iran have been on strike and are not expected back to work until Saturday at the earliest.

Once the plane lifted off the runway, however, tension disappeared. The evacuated expatriates joked, clapped their hands and -- in the course of the flight -- exhausted the plane's liquor supply.

One man and his wife paraded up and down the aisle wearing identical T-shirts emblazoned with "Civil War Sucks -- Tehran, 1979."

As the plane descended to Frankfurt International Airport, a middleaged man looked out the window and said: "Look, no gun battles. We're finally out of Dodge City."

Airline officials said, however, that if Saturday's evacuation is accompanied by as much harassment and delay, the several Boeing 747 jumbo jets scheduled for loading may not be able to depart because of the large numbers of people involved. Each 747 can carry about 400 passengers.

"If you thought today was bad, wait until tomorrow," said an airline official.