The giant pandas at the National Zoo stop eating and start panting if their two-bedroom unit gets above 70 degrees, so they remain exempt from President Carter's energy-saving edict raising federal thermostats to 80 degrees.

Picassos, computers and perishable archive documents also get special dispensation. But in most quarters of the federal bureaucracy, employes have adopted tropical dress and braced for a long, hot summer.

The reaction has not been as heated as it might have been. Washington's weather has been unseasonably cool so far this summer, except for unfortunates on the sunny side of certain buildings.

In any case, officials noted, most federl employes have been working in 78-degree summer offices since 1975 in the wake of the earlier energy crisis, so the recent change to 80 was not so shocking.

Some limits seemed in order, however, so federal officials have notified employes about a kind of discomfort policeman equipped with something called a psychrometer to measure temperature and humidity. They have also written into their personnel manual provisions for sending everyone home if things get too hot and sticky.

If an employe suspects the temperature in his office has risen above 83 degrees, the notice put out by the U.S. Office of Personnel Management instructs, he sould report it and the psychrometer will be dispatched to check it out, according to an OPM spokesman.

And Chapter 18 of the federal Personnel Manual states that employes could be sent home if working conditions get as bad as: 95 degrees with 55 percent relative humidity, 96 degrees with 52 percent relative humidity, 97 degrees with 49 percent relative humidity, and so on. There are no provisions should it began to rain indoors, the source added.

Most federal buildings are 30 or 40 years old, built long before OPEC and even the newer federal buildings, such as the headquarters of the FBI and HEW, are already "old" in terms of energy-saving design, according to Ted Leininger, director of building operations for the General Services Administration, the landlord of federal buildings.

HEW's Hubert H. Humphrey building, for instance, opened just two years ago, but it took seven years to design and build, and though it has "good central controls," Leininger said, "it doens't incorporate a lot of the things we'd put in today" to conserve energy.

Another problem is that, though the guidelines say 80 degrees, "you'll never get a building that's 80 degress all the way through," Leininger said. "There's a difference between the exterior offices and the inner core, the sun side and the shade side, So you'll get people walking in and saying, "Hey, how come your office is cooler than mine?"

Since warmer air carries more water vapor, humidity can also be a problem under the new regulations.

Some federal buildings have equipment that could reduce humidity without cooling, but they use extra energy and are prohibited under the guidelines, he said.