While Egyptian President Anwar Sadat startles the world with his campaign for peace in the Middle East, an odd little band of Americans remains on the alert here for signs of war.

The events of the past month may have changed history but they have not changed the routine of life for the 147 men and 14 women of the Sinai Field Mission.

From their watch stations on the forbidding windswept highlands between the Israeli and Egyptian front lines, they monitor every truck, jeep, person and even camel that enters their "early warning zone."

If there is any incongruity in their diligent lookout for truce violations at the confrontation line at a time when Israeli journalists are interviewing Egyptian officials in peace-happy Cairo, it has not made any difference in their work.

"It was really exciting to watch on TV" when Sadat landed in Israel, said Joe Smith, 28, an operations technician, "but our work is just the same."

The work is the full-time monitoring of the roads and passes of the desolate, inhospitable Sinai Peninsula.

With electronic underground sensors, infrared devices, radios and night vision scopes, they record all traffic through, into and over a 250-square-mile area inside the United Nations buffer zone, along the strategic Gidi and Mitla passes. Any unauthorized intrusion is immediately reported to Egyptian and Israeli military authoritias and to United Nations truce supervision forces.

The Sinai field mission, headquarters for the Americans, is an eerie world of fluorescent lights, paper towels. Ping Pong tables, Rice Krispies, electric typewriters and Washington telephone books, strangely out of place in the middle of a desolate wasteland, about 22 miles east of the Suez Canal.

It is a slice of America created by Congress and dropped into this unlikely place, to police the second Sinai disengagement agreement of 1975. Under it, Israeli troops pulled back to the eastern end of the passes and the Americans came out to see that both sides abided by the rules on traffic into the buffer zone, number of personnel and types of weapons.

The Ghanaians and Finns and Poles among the U.N. troops patroling the buffer zone are professional soldiers but the Americans watching the passes are civilians, "the nuttiest crew of people you could ever want to watch," in the words of Mary Doherty, an administrative officer sent by the State Department.

The nutty crew includes diplomats and dishwashers, communications technicians and drivers, a bartender and a social director, even a few old Vietnam hands like Edmund Sprague, and Indochina legend for his work with Montagnard tribesmen.

In conversations with two visitors - the first foreign correspondents from Cairo permitted to visit the field mission from the Egyptian side - mission hands listed a wife variety of reasons for agreeing to come here: money, adventure, opportunity, curiosity. But they all agreed that moral was high and said they felt they have played an important part in the change in the Middle East atmosphere that made Sadat's trip possible.

Far from feeling superflous when Israelis and Egyptians are suddenly exchanging peaceful visits, the mission staff "felt that our presence out here had contributed to what occurred," said David Cardwell, a Foreign Service officer who works as a liaison officer to the Egyptian and Israeli surveillance stations at the edges of the buffer zone.

The misson director, Leamon Ray Bunt, former deputy assistant secretary of state for operations, said the Sinai staff known that "even if there's speedy action peace, our presence will be needed for some thing - perhaps in a different location."

It cost nearly $30 million to build the camp and equip it with the goodies that make life tolerable for the staff - juke boxes and air conditioning, movie projectors and stereo sets, motel - style rooms and purified water - and another $12 million a year to run it.

Most of that is paid out not to the handful of U.S. government personnel but to the contractor who built the mission, E-Systems of Texas. The company's employees are identifiable by their bright orange uniforms. Since most of them were recruited in Texas, the place has a difinite Texas twang to it. A sign in the recreation hall says, "Please do not wear your boots while playing ping pong."

Texans run the laundry, cook the food, cut hair, tend bar and organize the social life, featuring Saturday night bingo, as well as operate the delicate electronic monitoring equipment that is the station's reason for being.

Most of them seem to like the place. According to Hunt, those who find it unbearable leave quickly and those who stay adjust quickly.

The E-Systems employees get a week out of the Sinai for every three weeks they work, going either to Cairo or Tel Aviv as they like. Pat Pampell, 29, the mission's barber and bartender, was in Israel when Sadat's plane landed and says she is still excited by that "dynamite scene."

Most of the others saw the historic trip on television, and by all accounts foiund it an exhilarating scene that has lifted the morale of the entire mission.

The two roads through the passes are the key to military movement across in Sinai, and it is along those roads that most of the seismic sensors, infrared sensors and manned watch stations are set. But there are also sensors squads or infiltrators might cross. These are known to the staff as "camel sensors," because those apolitical dun-colored beasts often wander in and set off the alarms.

Recording every movement through the area in little blips on graph paper that moves through monitoring machines, these sensors can determine the size, direction and velocity of anything passing through, from camel to tank.

Since the mission began operations on Feb. 22, 1976, the monitors have recorded 49 violations of the disengagement agreement rules on entry into the zone - 30 by Israel, one by Egypt and 18 unidentified.

All of them, Hunt says, have been either accidental overflights or "technical violations, not of hostile intent," which to him shows that the mission's presence has been successful. "It works because both sides want it to work," he said, "and because we do a good job. It's something we as a nation can be proud of."