By last night at the White House reception for the American Society of Newspaper Editors, the talk about Jimmy and Janet and the Pulitzer Prize hoax was starting to taper off. Some of the society's 1,100 members were even thinking about things like computer retrieval and next year's conference.

Michael O'Neill of the New York Daily News, for one, had his thoughts elsewhere. He takes over from Thomas Winship of the Boston Globe as ASNE president by the time the conference adjourns Friday.

"I was looking at this reception and hate a idea," O'Neill said, standing in the doorway between the Red Room and the State Dining Room. "Since next year's conference will be in Chicago, I thought we'd have our reception at the Cabrini Settlement House where Mayor [Jane] Byrne lives. She can host it and if she doesn't want us, I'm sure the other residents would be pleased to have us."

Certainly the residents of last night's reception site seemed pleased to have them -- even if some of the editors may not have known that the ASNE was picking up the tab.

"Nobody knows yet how much it will be because the bills aren't in yet," said a White House spokesman. An ASNE spokesman, however, estimated that it would cost around $10,000.

The man of the house, President Reagan couldn't get down to welcome everybody so First Lady Nancy Reagan, Vice President George Bush and every Cabinet officer except Secretary of State Alexander Haig did the honors for him.

"Nancy's going to kill any of these guys who try to push in and make him do too much," Bush said of the president, describing him as anxious to be out but in the meantime making telephone calls from the family quarters on his economic program.

Bush called the gathering "the second biggest group" of the week, the first being the Easter egg hunt with 21,000 kids.

"I don't know what you're all looking for, but I hope you find it," said Bush introducing O'Neill and Winship.

"Thank you, thank you, thank you," said Winship. "Today we're all Republicans."

Over the pate and quiche, some of the editors talked the one topic that has been dominating their conference since it convened Tuesday, the story of the bogus 8-year-old dope addict named Jimmy, how it happened and why it shouldn't have.

"What they're doing right now is playing intellectual incest," said Norman Isaacs, chairman of the National News Council.

"You [The Post] unfortunately gave everybody something to gossip about," said Burl Osborne of the Dallas Morning News, who wasn't completely certain that any newspaper could prevent it from happening.

"I can't guarantee that nobody will ever lie to me. We have fairly rigid rules about sourcing, but I'm not sure that's a source problem. Suppose the reporter came in and said, 'Okay, the boy is Jimmy Brown and he lives on Cronin Terrace'? Okay, you let it go at that."

Robert J. Cochnar, deputy executive editor of the San Jose Mercury-News, said it was "a matter of trust -- and trust is important here -- but that doesn't mean automatic trust" nor that one has to be a "perfect cynic."

Mary Ann Dolan, managing editor of the Los Angeles Herald-Examiner, thought the "only question to be asked" was what should have been done about the 8-year-old addict. "The discussion should have been: Are you sure you want to keep this secret? Have you thought about the kid? Should we discuss going to the police?"

Gerald Warren, editor of the San Diego Union, said he thought reporters wanted editors to be part of the process "because if you get into a court situation the reporter is going to stand alone otherwise . . . The shock of the thing has to lead all of us to take a look and see if we're stressing the right values in the newsroom."