George Clooney, Gladys Knight, Bono and the rest of U2 were on hand Sunday in our nation's capital to receive their Kennedy Center Honors for contributions to the arts over the course of their lives ... and they all dressed to impress for the swanky get-together.

Other honorees included composer Tania Leon and Christian singer Amy Grant -- they all lined up for tons of photos and took in the applause as JB sang their praises. At one point, he even singled out Gladys specifically and made a little pun about a classic tune of hers.

As for the rest of the bunch ... POTUS called them all "truly exceptional" during the reception -- noting Clooney's exceptional on-camera roles over the years, not to mention his philanthropy. And as for U2 ... well, let's just say Joe's a fan, going so far as to call them poets of our time.

BTW, it wasn't just these celebs who were in the house ... Julia Roberts was there, as was Don Cheadle, Richard Kind, Matt Damon, Sean Penn and others. So, yeah ... BIG turnout.

There's bits of video trickling out from the actual ceremony -- but the whole thing was properly recorded and is going to air in full later this month. It may even include performances from some of the musical acts ... time will tell.