Almost half of Newsweek's subscribers may be surprised this week to read that the Camp David summit appeared to be ending in a depressing stalemate.

By 11 p.m. Sunday, after the joint announcement of the negotiating breakthrough, Newsweek had already printed 1.435 million copies of its Sept. 25 issue, with a cover line: "The Summit: What Next?" At 2:30 a.m., four small jets left New York for different printing locations with three made-over pages for the cover story. The remaining 56 percent of the 3.3 million press run bore the inside headline: "The Breakthrough."

Over at Time, they were playing more cautious poker. On Saturday the presses had begun spinning out about 4.5 million covers proclaiming "After the Summit," noncommittal enough to cover most bets.

But Time waited to print the body of the magazine until 7 p.m. - about five hours late, at a cost of $10,000 an hour - "Because we thought they'd break up the meeting in late morning and we'd have the whole story," according to associate publisher Reginald Brack.

By 11 p.m. the presses wer stopped, after 150,000 copies of Time had been completed. Within four hours the entire magazine was rearranged, so that four pages of additional copy and photographs could be inserted.

All this cost Time and Newsweek about $10,000 an hour for down time on the presses: about four hours at Newsweek, about 10 at Time, as well as the costs of getting new plates out to about half a dozen printing locations. Both magazines normally begin printing in early afternoon on Sunday; Time's first revised copies weren't finished until late Monday morning, which gave Newsweek an early lead to newsstands.

"It's who's there first that matters," says an executive at Newsweek, who's betting that the late arrival of Time - usually on stands by noon Monday, delayed this week until Tuesday morning - may help Newsweek's early sales substantially.

At Time, Brack simply says the delay "gives us the opportunity to present the full story to our readers."

The real loser in all this may have been photographer Richard Avedon, who was slated to be Newsweek's cover subject in conjunction with the opening of a show of his fashion photography in New York last Thursday.

"We pulled that cover Saturday night," says Newsweek manufacturing director Todd Rankin. "It wasn't a major expense, but the editors decided that the (then) stalemate at the summit was more important. We don't know if we'll ever use the Avedon story now."

Changeovers are not uncommon at major news magazines, although huge down tome expenses and distribution problems prohibit stopping the presses for more than a few minutes to make minor changes.

"We might go in and change a Milestone," says Brack, refering to Time's column of that name. Rankin recalls a last-minute change when the Patty Hearst trial was in progress.

At each magazine, an executive expressed some suspicion that the White House had pulled a grandstand play at an hour when there was little time to appraise the proposals seriously.

"We felt a little bit that we were being used," says a high-ranking Time official. "We're used to having so many leaks that we know exactly what to expect. This thing couldn't have come at a more costly time." A Newsweek executive concurs: "It was almost like Nixon was back in the White House, trying to kick back at the media."

"When it rains it pours," says Brack. "We've had three last-minute cover switches in the last month.

"The worst was when the Pope died. We had 2 million copies of a cover on black holes printed, and we had to dump them. We had another cover printed and then the new Pope was elected and we had to dump that cover. Those two cost us several hundred thousand dollars."