"Face the Nation," a public affairs staple of the Sunday CBS schedule since November 1954, will be canceled by the network sometime this summer and will be replaced with an entirely new format by the fall.

George Herman, who has moderated the program since January 1969, was notified of the decision last month and it had remained a well-kept secret even at the network until earlier this week.

That's when a CBS News technician overheard CBS White House correspondent Lesley Stahl confide to a friend in a phone call that she is due to replace Herman as moderator on the new program and the cat, as they say, was out of the bag.

CBS News officials in New York and Washington yesterday refused to discuss details of the new program or a precise schedule for the phase-out.

One did confirm that the name will be retired with "Face the Nation's" final broadcast.

A network source said "Face the Nation" will end its run sometime this summer and that plans are to launch the new format no later than August in order to get the kinks out of the new show before the fall and its larger audiences.

Nobody at CBS News will say so, but it is clear that "Face the Nation" is a casualty of the growing success enjoyed by ABC's "This Week With David Brinkley," with its varied format and one-hour length.

"Brinkley" debuted in November 1981, replacing a moribund "Issues and Answers."

After 11 weeks of the first quarter of 1982, NBC's "Meet the Press" was still the clear leader among the three network interview shows with a 4.7 Nielsen average and a 15 percent audience share, but the Brinkley show had already climbed to a 3.9/13, while "Face the Nation" trailed with a 3.3/11.

For the same period this year, "This Week With David Brinkley" is far ahead with a 4.2/13, compared with "Face the Nation's" 3.2/10, just barely in front of "Meet the Press" with 3.1/10.

For all the scanty audiences, however, "Face the Nation" has always been considered a major profit center for CBS News.

One source close to the program said yesterday, "I think it costs CBS about $200,000 a year to produce, and longtime sponsor IBM pays at least $2 million a year for it. I think it just got tired."

Herman, a 39-year CBS News veteran, said yesterday he regrets the phasing-out of the program but insisted, "I've no complaints."

Friends of Herman at CBS yesterday expressed concern that the end of the program could spell finis for his long tenure at the network.

He has been working without a contract since January.

But Herman said yesterday, "I have no plans to retire," and a CBS News executive in New York said that "although George is nearing 65, he can work at CBS just as long as he wants to." Moving Right Along

ABC News has lured Rita Flynn away from CBS News . . . although she won't report for new duties as a general assignment correspondent at the ABC bureau here until June. . .

The move is not unexpected. . .

The current ABC News bureau chief here is Ed Fouhy, who had hired Flynn from WFAA in Dallas-Fort Worth in 1980 when he was with CBS News. . .

Fouhy is known to be enthusiastic about her prospects. . .

Flynn, who had covered the State Department and was on general assignment with "CBS Morning News" most recently, was reportedly unhappy with her treatment at CBS News following an incident in which one of her stories appeared on "CBS Evening News" without crediting her. . .

However, both CBS News president Van Gordon Sauter and executive vice president Ed Joyce have recently urged her to stay with the network. . .

And "CBS Evening News" anchor and managing editor Dan Rather last night praised Flynn as "a good person and a good reporter. I wish her well". . .

Ted Koppel is sitting in as anchor on "ABC World News Tonight" for the next week or so while anchor Frank Reynolds lets a stress fracture of his left leg mend. . .

Reynolds apparently first injured the leg in an accident at Key Biscayne in January and hurt it again here in a fall during the Big February Snowfall. . .

After limping around with a cane for a couple of weeks, he finally went to a doctor whose X-rays disclosed the fracture. . .

At least four NBC affiliates will not carry "Special Bulletin" Sunday night but apparently only one, WTMJ in Milwaukee, has dropped it because of the controversial nature of the drama. . .

"Special Bulletin" tells the fictional story of terrorists threatening to blow up Charleston, S.C., with a nuclear device unless their demands are met. . .

But the story is told with a series of realistic newscasts from the "RBS Network" and some fear that the average viewer may take the telecast too seriously. . .

NBC Entertainment . . . with prodding from NBC News . . . has now placed 17 different disclaimers throughout the two-hour drama reminding viewers that it is only fiction. . .

NBC News, moreover, will not include a real "NBC News Capsule" during the program, and Channel 4 here, an NBC-owned station, will also forego its usual 10:30 Sunday night cut-in on local news. . .

In a statement, NBC News president Reuven Frank said, "The only concern of NBC News was that 'Special Bulletin' might be confused with a news program. We agreed on various steps to insure that the average viewer will not be misled in that way". . .

Meanwhile, WBZ in Boston and KXAS in Dallas-Fort Worth are both preempting "Special Bulletin" for basketball games, and KTVY in Oklahoma City will substitute the movie "Oklahoma!". . .

A spokesman for NBC said yesterday that with the added disclaimers inserted into the program there "is still an outside chance" the Milwaukee affiliate will reschedule the nuclear drama. . .

"The A Team" earned a solid 32 percent audience share in the national Nielsens Tuesday night and shortly thereafter NBC Entertainment decided to renew the light-hearted, if violent, adventure-drama for the 1983-84 season. . . And Finally

No official announcement yet, but it's increasingly clear that ABC News will expand "Nightline" to a full hour fairly soon as the division dumps "The Last Word" . . . Phil Donahue, Gregory Jackson, low ratings and all. . .