Willard Scott, one of the most popular and enduring personalities in Washington broadcasting, said yesterday he is leaving his post as weatherman and resident cut-up at WRC-TV next month to become the daily weatherman on the NBC network's "Today Show."

Scott, 45, has been the station's weatherman for a decade and was rated in a recent survey as the most recognizable figure in local television. Officials at the NBC-owned station -- also faced with the defection of news anchorwoman Sue Simmons to WNBC-TV in New York -- could not be reached for comment on what Willard's loss will mean in the hotly fought local television news wars.

"There's nothing negative about this -- no lawyers, no hard feelings." Scott said from his farm in Paris, Va. "It's not that I'm bored here. It's just that the opportunity's there and I'd be a fool not to take it."

"The way I look at it," Scott said, "I'm there to fill the void created when J. Fred Muggs left."

J. Fred Muggs was a chimpanzee who costarred with Dave Garroway during the dawning of "Today" on NBC in the 1950s.

Scott had an on-air audition for the "Today" job for two weeks earlier this month. NBC News president William Small was impressed with his jovial folksy performance, insiders say, and gave Scott a call on Christmas Eve.

"He told me, 'I want you up here Wednesday morning to discuss your career,'" Scott said, "and I had a feeling NBC wasn't going to spend $104 on shuttle fares to tell me I was through."

As of yesterday, two "Today Show" producers said they had not been informed that Small had selected Scott to replace current weatherman Bob Ryan. But one of them, Steve Friedman, said of Scott, "He's funny, he gives you the weather, he's a human being, and we could do a lot worse."

Although still the ratings leader in its early morning time period, the "Today Show" has seen its dominance erode in recent years to competition from ABC's "Good Morning, America." While "Good Morning" rose 26 percent in Nielsen ratings from 1978 to 1979, "Today" declined by 11 percent during the same period.

It is believed that the addition of Scott may help humanize the "Today Show" and make it more competitive with the looser, chummier "Good Morning." s

Scott said that by the end of the first week of this "Today Show" tryout, "the crew began responding, and I could see where everything might jell and give the show a light touch, which is what it needs, I guess."

Although he will live in New York during the week, Scott said, he will not desert the Washington area and plans to keep his Virginia home for weekends. He and his wife, Mary, have two daughters.

Scott started in broadcasting here at the age of 16, auditioning for NBC radio and beginning a career that has lasted 29 years with the company. For 17 of those years, Scott was half of Washington's most popular disc jockey duo, "The Joy Boys," but he and long-time partner Ed Walker were jettisoned when WRC radio switched formats in 1972.

By 1975, Scott was making an estimated $80,000 a year at WRC-TV. He declined to discuss details of his new network salary, but it is reportedly in the $200,000-a-year range. Scott says he signed a five-year contract with a one-year guarantee. That means he has 52 weeks to ingratiate himself with his distinctive brand of tomfoolery on the early morning national audience.

Since predicting the weather in Washington is a patently inexact science anyway, and Scott is not a licensed meterorologist, he devoted part of his nightly air time on WRC to plugging local charities and community activities. Members perpetually flood the station with jams and jellies in the hope of getting Willard's attention on the air.

Scott said he hopes to continue taping these "public service" bits for use by WRC even after he goes to New York. "If I bomb up there, at least I can still be on the air here," he said. But whether the practice can be transferred to the national arena is doubtful; after mentioning North Carolina honey on the air one morning, Scott and NBC were deluged with samples from other parts of the country.

A network official complained that all the honey was interfering with operations, Scott said.