WHAT OLYMPIC sport is more grueling than the marathon, more demanding than the decathlon, more perilous than Alpine skiing and wilder than the luge?

Obviously, television.

The televising of any Olympic Games, winter or summer, is itself an undertaking of Olympian proportions - a high-stakes, high-pressure business in which not all that glitters is gold medals.

The American public has come to regard the Olympics as a quadrennial TV spectacular as lavishly covered as a presidential election night, as polished and dramatically gripping as "Roots."

For the American Broadcasting Co. which has made its reputation as an innovative leader in sports television largely through its telecasts of six of the last eight Olympic extravaganzas, production of 50 1/2 hours of the XIII Winter Games from Lake Placid, N.Y., next Feb. 12-24 should be a relative snap.

ABC's experience will make it so, despite literally chilling problems of iogistics, the cable-chewing tastes of the wildlife on Whiteface Mountain, and the strain of having to provide separate customized pictures for the U.S. and foreign audiences.

For newcomer NBC-TV, which in 1976 outbid ABC and CBS in the giddy, celebrated auction for exclusive U.S. TV rights to the 1980 Summer Olympics, providing 150 hours of interesting programming from Moscow next july 20 to Aug. 3 is a more adventuresome, uncharted challenge.

There will be no wind-chill factor of 60 degrees below zero in Moscow, no danger of porcupines gnawing on miles of carefully laid cable, but there is the clear and present danger of runnig out of visually fascinating events to cover. And who knows what political and bureaucratic evils lurk the hearts of the Soviets. The peotential for unforseen disaster in the televising of the first Olympics held behind the Iron Curtain is great.

"Certainly, no one has ever done anything like this from an East European country before," said Alan Baker, NBC's vice president for corporate information.

"Everybody hopes that politics won't get involved at the ballpark. We could kill ourselves from now until next summer with 'what ifs.'"

NBC has already spent $87 million, including $37 million in rights fees to the Soviets and the International Olympic Committee, to obtain and gear up for its unprecedented Olympic coverage, which doubles the 75 hours of the 1976 Summer Games that ABC televised from Montreal.

NBC has been working on the Olympics literally since the day it secured the broadcast rights, and will spend another $20 million to $30 million in production costs. The network has already poured $50 million into the construction and equipping of the sophisticated broadcast center in Moscow that will send pictures around the world.

NBC already has sold $170 million worth of commercial time on its Olympic telecasts.Twice it has raised the rates, but still a complete sellout well in advance of the first telecast is guaranteed.

The minimum package an advertiser can buy is $1 million, which buys 6 1/2 minutes of time rotated, at NBC's discretion, between morning, afternoon, prime-time and late-night viewing periods. The average cost for advertisers to get their message across is $130,000 per minute.

"It has been more profitable than anybody expected it would be," said Baker.

NBC will have 45 cameras at 14 venues in Moscow to supplement the 140 cameras the Soviets will use to provide the world feed. In addition, the U.S. presence will include enough manpower and equipment to do justice to a sizable military operation. There will be 360 NBC technical and production personnel in Moscow, plus 300 support personnel - a total of 660 men and women with everyday duties and responsibilites.

The general in charge of this operation is Don Ohlmeyer, executive producer of all NBC sports, who was part of five Olympic efforts for ABC before being wooed over to NBC by a reported $400,000-a-year salary and the opportunity to have overall responsibility for the biggest challenge in the history of American sports television.

What can we expect to see? In 150 hours, a little bit of everything, including Dick Enberg serving as overall host.

"There's no question that American viewers like to see how American are doing in the various sports," said Baker. "We know a good deal about U.S. prospects in track and field, gymnastics basketball, swimming, sports like that. We're not so sure about some others like volleyball and the equestrian and shooting events. We're waiting for the trials, and our researchers keep us apprised on developments so that we can plan what Americans would most like to see.

"We know that there will be much more focus than ever before on women in sports, and not just American women."

Because of the seven-hour time difference between Moscow and the Eastern U.S., much of NBC's coverage will be on a tape-delay basis. This should make for polished, glossy production especially since Ohlmeyer is recognized within the industry as a genius at "post-production" techniques.

A number of events will be televised live, especially on weekends, because there will be competition in Moscow until 10 p.m. each evening (3 p.m. on the U.S. East Coast). Opening and closing ceremonies will be shown live.

NBC hired Bud Greenspan, who has produced award-winning documentaries for public as well as commercial television, to prepare a series of feature pieces on leading atheletes from various countries - an adaptation of ABC's acclaimed "up close and personal" treatment of Olympians.

While no one can argue with Baker's contention that the 150-hour Summer Games package is "the most ambitious television sports event ever," the Winter Games coverage has its own peculiar problems. ABC has had a production and engineering team at Lake Placid since December 1976, working to solve them.

Whiteface Mountain, site of the Alpine events, has four separate slopes that must be laid with underground cable to provide "start-to-finish" coverage of races without endangering the skiers. ABC laid 33 miles of cable at Whiteface before last winter's World Cup skiing coverage, but had to pull it all up because it learned - from bitter experience - that porcupines and other animals living on the mountain chew up TV cable during the spring thaw.

A complete TV sports center, with two control rooms and 20 videotape machines, has been built in Lake Placid. It is from here that the activities of 800 ABC employes will be coordinated, and pictures provided not only for the U.S. audience but for all international networks televising from Lake Placid.

Since there is never more than one event going on at once at the Winter Olympics, and the 1980 Games take place in the Eastern U.S. time zone, the schedule is fairly well dictated by the events schedule.

ABC will provide prime-time, weekend, late-night and daytime telecasts, starting with opening ceremonies on Feb. 13, 1980, which will be shown live and then repeated at night.

ABC will be televising seven more hours from Lake Placid than it did from Innsbruck in 1976, but already all commercial time is sold out, at rates comparable to NBC's for the Summer Games. Why are advertisers so eager? It is estimated that 180 million people, or 85 percent of the total U.S. population, will see some part of the 13 days of coverage from Lake Placid. CAPTION: Picture, Dick Enberg