"Agronsky & Company," as close to a Washington television institution as you'll find, is getting a new host and a new title come Jan. 2.

After 18 years as moderator of the program that bears his name, and 47 years in the industry, Martin Agronsky has decided to call it quits. He has told Post-Newsweek Stations Inc., which produces and distributes the public affairs program, that he will not renew his contract at the end of the year.

When the roll is called Jan. 2, WUSA anchor Gordon Peterson will be at the helm of the renamed "Inside Washington," along with regular "Agronsky" panelists James J. Kilpatrick, Carl T. Rowan, Hugh Sidey (all three of whom have been on the program with Agronsky since its introduction in 1969), Elizabeth Drew and Strobe Talbott.

The program is a fixture at 7 p.m. Saturday evenings on WUSA, and is also aired on the four Post-Newsweek stations in Detroit, Miami, Hartford and Jacksonville, Fla., as well as 50 other markets around the country, including Los Angeles, San Francisco, Boston, Houston, Denver and Atlanta.

Peterson, who moderated "After Hours" with Tom Braden and Pat Buchanan for a couple of years on Channel 9, recalled yesterday that "Agronsky & Company" "started about the time I got here. I love it. It sounds funny to say, but I'll miss Martin on that program -- I may have to stop watching it."

Peterson called Agronsky "part of the real estate around here -- he's like one of the monuments in Washington. The people on that show are like family."

Yesterday, Agronsky was in a reflective mood. He said he had been thinking about quitting the show over the last 18 months.

"I didn't come to this decision casually," he said. "I've been in the business since I was a war correspondent for NBC in 1940 {he covered the British Army in Greece, Turkey, the Middle East and Singapore and Gen. Douglas MacArthur in Australia}.

"I thought about it a hell of a lot, talked it over with my wife and I finally made up my mind really in June. We're leaving at the top, the ratings are fine and I decided when January '88 comes I'll have been in it long enough. I really didn't want to have a commitment anymore and the only way to stop having a commitment was to stop having the show."

He said he had kept his secret from the other regulars on the show. He is thinking about writing a book or perhaps doing a series of documentaries, but for now, "I really don't know what the hell I'm going to do."

He recalled that when Post-Newsweek vice president Jim Snyder (then as now executive producer of the program) first proposed he do the show, "I didn't think Saturday night at 7 p.m. would work. Nobody had ever done it. But I guess we caught the mood of the time."

Joining Sidey, Kilpatrick and Rowan on the first programs was Chicago Sun-Times White House correspondent Peter Lisagor, whose acumen and sense of humor visibly helped the sobersides on the program relax.

"When Peter died in 1976," Agronsky recalled yesterday, "he wasn't replaceable. But then we brought in George Will and he did a first-class job before we lost him to ABC News. Then Liz Drew joined us after George left and we just kept building. It's been a marvelous experience."

Agronsky's distinguished career took him to Washington and ABC News in 1943. After 12 years he rejoined NBC. In 1962 he moved to CBS News and in 1967 began five years with PBS here, working "Agronsky & Company" once a week starting in 1969.

Peterson, who remains premier news anchor in this market, said that when Snyder (who had been his news director when Post-Newsweek owned Nine) approached him about replacing Agronsky, "I grabbed at the chance to moderate the show. I love to do that kind of stuff."

Also in the News ABC's "Once a Hero" is now Once a Series -- and the first major network casualty of the new season ...

ABC announced yesterday that "Once" had its last outing Oct. 3 and will be replaced on Saturday, Nov. 7, in the 8 to 9 p.m. time slot by an adventure hour called "Sable" ...

A series of special programs will alter ABC's Saturday schedule in the interim. They include the Oct. 24 debut on ABC of "All Star Gala at Ford's Theatre" and repeats of "A Carol Burnett Special ... Carl, Carl, Whoopi & Robin" and the Halloween comedy thriller "The Midnight Hour" ...

"Once" had failed thrice on the network, premiering Sept. 19 to a 5.1 Nielsen rating and a 10 share, then falling to a 3.7/7 and concluding this past weekend with a 4.6/9, finishing either last or next to last in national ratings each week ...

"Sable" stars Lewis Van Bergen as a mysterious man who leads two lives -- as Nicholas Flemming, sophisticated author of children's stories, and as Jon Sable, "a passionate man of action who risks his life helping others" (you're already Captain Airwaves' kind of guy, Lew) ...

Aiding Lew in all this will be Rene Russo as his glamorous literary agent and Ken Page as Joe (Cheesecake) Tyson, a blind computer hacker ...

Sources at CBS News yesterday confirmed that as many as 60 to 70 people will be hired for the reconstituted CBS morning news, which returns to a three-hour broadcast on Nov. 30 ...

No word yet on whether some of those victimized by last spring's Friday night massacre, which eventually claimed 230 positions at CBS News, will get jobs back. The total is believed to include some in-house transfers from other programs ...

CBS News, by the way, made it official yesterday: David Corvo, who has been in charge of the 90-minute very early "CBS Morning News," has been named executive producer of CBS News' morning broadcasts, including the new two-hour show anchored by Kathleen Sullivan ...

Sixteen of NBC News' top correspondents, including Tom Brokaw, John Chancellor, Richard Valeriani and Connie Chung, yesterday sent a letter to NBC president Bob Wright urging him to settle the 15-week strike against the network by 2,800 members of the National Association of Broadcast Employees and Technicians -- as NBC and NABET negotiators met in Washington ...

Another 18 correspondents also signed the letter "by proxy," to show their support of absent employes. The letter claimed "the spirit of NBC is being sapped by the strike" ...

Responding for management, NBC executive vice president M.S. Rukeyser yesterday said "the strike has been a terrible burden for everybody at NBC, both inside the company and on the picket line. We hope the talks now going on in Washington can lead to a settlement that bring our company back together again" ...

Dennis Swanson, president of ABC Sports, is expected to return to the job the week of Nov. 2. He's been on leave to be with a son in California, who is recovering from injuries suffered in a serious accident ...

Game one of the National League baseball playoffs Tuesday averaged a 15.5 Nielsen rating and a 26 percent audience share between 8:22 and 11:08 p.m. ...

For the night, ABC led with a 20.1/33, NBC averaged a 14.9/25 and CBS had a 13.7/22 (each rating point represents 886,000 TV homes) ...

And Finally Captain Airwaves thought the following item was so interesting yesterday, he is repeating it, almost word for word, again this morning (which is a long away around to admitting the Caped One had the date wrong yesterday):

The House subcommittee on telecommunications will see a demonstration of the latest in high-definition television technology this morning starting at 9:30 ...

High-definition is the next Big Thing in TV reception, increasing the 525 lines for a picture on current sets to more than 1,100, providing much sharper pictures ...

Today's closed-circuit demonstration in Room 2123 of the Rayburn House Office Building is being conducted by CBS engineers and the National Association of Broadcasters. In addition, PBS has arranged for an international satellite transmission of an HDT signal ...

Chairman Edward Markey (D-Mass.) will also hear from representatives of the NAB, the National Cable Television Association, the Association of Maximum Service Telecasters and proponents of various systems under development including NBC, which this week announced a technology breakthrough, and NHK, the Japanese TV network ...