Outside it was a humid and scorching 93 degrees; inside it was a cool and shady 78. The National Zoo's gorillas, some of man's most intelligent kinfolk, knew when to stay put.

The National Zoo opened the quarter-acre yard of its new Great Ape House for the first time yesterday, giving Nikumba, the oldest of the zoo's gorillas, the run of the land after more than 20 years in capitivity. For M'Wasi and Femelle, two 18-year-old females, it was their first ever opportunity to roam in an open space through lush grass.

Whether it was the weather -- as suggested by zoo keepers -- or the natural shyness of the animals, the new yard, even with its sunken pool, was not enough yesterday to lure the apes away for long from the interior comforts of the new $2 million structure, which opened in April.

Instead, the three gorillas spent most of their three-hour "outdoor recess" alternately peering through the doorway and then trying to pull the door closed. The total time spent in the yard by all three was about five minutes.

"They don't rush themselves," zoo keeper Walter Tucker said. "This is the first time they've been on grass. The feel of the earth is a big change from the cement floors they're used to walking on."

"I'm really surprised Nick came out," zoo mammalogist Miles Roberts said excitedly. "He doesn't like to go through new doors, new situations. He's very reluctant."

The zoo's Great Ape House is complete with skylights, solar panels, air conditioning and a portable television that is tuned to cartoons, sports events and any show that has a lot of action, according to Tucker. Sometimes, he said, the gorillas even watch the daytime soap opera "All My Children."

"We just turn the dial until they see something they want to watch," Tucker said.

The structure designed by the architectural firm of Wilkes and Faulkner, is part of the National Zoo's effort to provide natural environments for its denizens. The Lion and Tiger House was the first such building and opened in 1975. The Reptile House, another cement, glass and grass complex, is scheduled to open in September.

Zoo officials hope the natural surroundings will help the apes, which are an endangered species, form social groups and -- perhaps -- even reproduce. Four gorillas have been born at the zoo since 1972, all of them sired by Nikumba.

Tomoka, Nikumba's first offspring, is the only other gorilla now at the National Zoo. He has separate quarters inside the complex and will get his turn in the yard after being gradually introduced to the other apes in the indoor quarters first, Roberts said.

The gorillas' lack of enthusiasm for the new yard was no surprise to zoo keepers.

"A clap of thunder could scare them back in for months. Or, if they have good experiences outside they could be used to it in a matter of weeks," zoo keeper Melanie Bond said. "But we have no way of knowing. We didn't expect instant success."