"He treats you just like you were his next-door neighbor," Beatrice Burstein said after meeting President Reagan at the White House yesterday. "And his sense of humor!"

Her sister-in-law Ann Burstein jumped in: "After I shook his hand and he moved away, I followed him. He shook my hand again and said, 'I met someone who looked just like you a minute ago.' Isn't that great?"

The Bursteins and about 448 other people were laughing at the president's jokes at a reception for members of the James Smithson Society and the National Board of the Smithsonian Institution. Both help the Smithsonian in a very basic way--the society donates money and the board tells the institution how to get other people to donate money. They often overlap.

But few mentioned anything so crude as money at the White House. Instead, they complimented each other and talked about how "beautiful" the Reagans were and how "kind" the donors were and how "exquisite" the White House was.

"As I came over here today, I wondered to myself, 'Why in heaven's name are the Reagans being so nice to us?' " Smithsonian secretary S. Dillon Ripley told the group. "And suddenly I realized it is because we are all very nice people, and the only thing nice people can do is be nice to each other."

Then the president thanked the crowd for helping the arts avoid "totally relying on the government." Vice President and Mrs. Bush stood behind Nancy Reagan, who stood behind the president. When the Reagans arrived, the two couples hugged and the Reagans welcomed the Bushes back from their Eastern European trip. The crowd smiled at them like proud parents watching their children at a first piano recital.

Ripley, who will retire next year, later said his as-yet-unnamed successor will have to decide whether the institution should establish a "museum of man--that's mankind, of course."

The secretary's wife's cousin was watching him, smiling so warmly she seemed about to melt.

"They will never find a replacement who's as good as you," she said.

"That's a lot of hoo-ha and horse feathers," said the secretary.