Great art can take a while. It took 10 years for the National Gallery's new East Wing to built, and it took a day of waiting yesterday to get Henry Moore's new 15-ton bronze sculpture into place.

First it looked as if the crane wouldn't clear the building's lintel. Then it looked as if the 80-year-old sculptor might fail to show in time.

"It's going to be a tight squeeze," said a worried gallery project director David Scott as the big blue crane struggled heroically with the first half of Moore's "Knife Edge Mirror Two Piece." Architect I. M. Pei, Mrs. Pei, project architect Leonard Jacobson, gallery officials, visitors and the press looked on.

It had been planned that all would be ready for the arrival of Moore, expected in on the 12:10 Concorde from London. By 2 p.m., however, the sculpture still dangled in the air and Moore had not arrived.

Suddenly a taxi pulled up, depositing a couple into the arms of Pei. Photographers mobbed them, assuming Moore had arrived. They turned out to be concert pianist Byron Janis and his wife Maria (daughter of Gary Cooper), invited down from New York by Pei to see the building and test the acoustics with a grand piano placed in the atrium.

Then a trim but sturdy figure approached unceremoniously on foot from across the plaza, his tie and jacket off and his sleeves rolled up, a walking stick in hand.

I.M. Pei rushed out to greet Henry Moore.

"Henry, welcome, I'm afraid we are not as efficient as the Concorde!" Moore was unruffled by the state of things.

"Getting the sculpture installed is I.M.'s problem, not mine," he remarked.

Moore conferred with the crane operators and went into the building for his first look at the completed interior. He was obviously moved.

"It's a shame Sandy couldn't have lived to see that," he said, looking up at the giant Calder mobile moving slowly above.

He was less expansive about the work of his former student Tony Caro when Gallery Director Carter Brown led him to Caro's steel "National Gallery Ledge Piece."

"That little bit hanging over the edge is from his table sculpture, eh?" asked Moore, after staring for a while.

Brown diplomatically added a few words in behalf of the controversial piece and asked Janis to play.

Janis obligingly sat down and played a few chords, moving on to a rendition of Moussorgsky's (sp) "Pictures at an Exhibition."

Pei darted up the stairs, grinning like a schoolboy, as he listened to his building sing for the first time.

"I.M., I think you've built yourself a concert hall," said Maria Janis. "If so, it's just a fluke," Pei said, delighted that there was no echo. "It's probably because there are no parallel walls to make the sound bounce back and forth."

Meanwhile, outside the building, the crane operators had re-rigged the sculpture and had it poised over the appointed spot.

Moore emerged, produced a drawing marking the exact touchdown points, and watched as his largest sculpture to date finally touched down.

Of course it still needs to be cleaned up and polished," he explained, like any automobile that's just had a long trip.

And was he disturbed by the troubled the work had encountered on the way - the dock strike in Southampton, the complications with the crane?

"What troubles?" asked Moore. I just can't wait to see the piece installed and shining in the full sunlight."