It could easily have been Frank Gifford's worst year on ABC's "Monday Night Football." Instead it has been his best.

Heading into the 18th season of "MNF," television critics, as usual, were nipping at the heels of Gifford, the show's senior man. He was in his second season as a color commentator, rather than the more familiar play-by-play role and, to top it off, a third sportscaster with a dominant personality was being squeezed into the booth beside him. Not to mention that the season had been fractured by the NFL players' strike.

But Gifford, showing much of the same steadfastness and adaptability that landed him in the Pro Football Hall of Fame, has played the hand that was dealt him and laid a fistful of aces on the table.

It's no longer a World Serious every Monday night. It's a football game. And Gifford, Al Michaels, and the newcomer, Dan Dierdorf, have fun doing them. Michaels is one of telecasting's most respected play-by-play men. Dierdorf, the St. Louis Cardinals' former all-pro offensive lineman, brings a dynamic style with his sometimes pointed commentary. All of this has brought out pointed comments and surprising humor from Gifford.

From Gifford's standpoint, what you see of him and Dierdorf is what there is. "He's a funny guy and we have a lot of laughs going to practices, meetings and meals," said Gifford. "It's carrying over into the telecasts in a lighthearted way."

Gifford has always been happy doing NFL games. He spent his first 15 years in the play-by-play role, starting the second year of "MNF," but describing the action didn't leave him much elbow room for humor. "I enjoy the game and I enjoy what I'm doing," he said.

Gifford has taken his share of shots from critics, but he always ranks high on fan-opinion polls. Viewers like him because he comes off as the true-blue straight-arrow that he is, honest, earnest, sincere and amazingly good-looking for a 57-year-old grandfather.

"I don't pay attention to the critics. I have to please the audience," he said. "I know what I am. That's more important than reading what others think. I know this game. I've always studied it and I continue to do my homework."

Gifford noted that he probably spends more time preparing to televise a game than he did preparing to play them. It's paid off. As first a player, then a play-by-play announcer and analyst for the past 36 years, he's earned the nickname "Faultless Frank."

Gifford started sportscasting 30 years ago while still playing for the New York Giants. In 1976-77, he won the Emmy as television's Outstanding Sports Personality. A host on ABC's "Wide World of Sports," Gifford has covered three summer and three winter Olympic Games since 1972 and will cover the 1988 Winter Games in Calgary.

A year ago, he married Kathie Lee Johnson, who with Regis Philbin hosts WABC's top-rated morning show in New York. Gifford fills in for Philbin about three or four weeks a year. He has also served as a guest host of ABC's "Good Morning America."

But he is best known for his long-running stint on "MNF," where he's become television's marathon man. By the end of this season he will have worked 336 prime-time football games. That's 1,120 hours, using 3 hours 20 minutes as the average duration for a game. Add six Olympiads and other prime-time specials and Gifford has worked more hours of prime-time television than anyone in the business, more than 1,200 hours.

"I'm kinda proud of that," said Gifford. "That's more than 40 days and 40 nights (960 hours). I guess you can say that's more time than Noah spent on his ark."

"The Ed Sullivan Show" ran for 23 years, which at the rate of 52 hours a year would still be under 1,200. (The first and last years, the show was on only for six months, and there were severa weeks over the years that the show was not scheduled.) Larry Hagman and "Dallas" would have to stay on the air for 40 years to match Gifford's time on "MNF."

Last year, to make room for Michaels, Gifford switched to analyst. This year Dierdorf moved into the booth as ABC returned to the three-man format used in the days of Don Meredith, Howard Cosell, Fred Williamson, Alex Karras, Frank Tarkenton, O.J. Simpson and Joe Namath.

They came and they went. Frank Gifford stayed. He took over for Keith Jackson, who did the first season of play-by-play on "MNF." At the time, ABC sports monarch Roone Arledge admitted that he wanted to sign Gifford from the outset but had to wait a year while Gifford was under contract to CBS.

Gifford's 16th season should have been a banner year for him and for ABC. The schedule was great -- "without a doubt the best I've ever seen," said Gifford -- starting with the Bears and Giants. But a Cleveland-Denver game, last year's AFC championship pairing, was lost to the strike. And the three replacement games didn't help, including a Washington-Dallas game that should have been a season milestone.

Working the strike games was a varied experience. "The tough one was the first {49ers-Giants} -- a little awkward," said Gifford. "We knew nothing about the players. It was an interesting contrast as we went along for three weeks. But fan interest has been affected by the strike. It's a shame it happened."

Meanwhile, ABC had taken on Dierdorf, Gifford's 10th booth-mate. The network hadn't felt any urgency to add a third person to the line-up, reports said, but when Dierdorf and CBS were unable to come to contract terms, he was signed.

It compounded an already difficult situation for Gifford. His switch last year from play-by-play to analyst was "difficult for me, although at the end we were doing fine. Even the critics toned down."

(Monday Night Football ratings were up 15.8 per cent in 1985 after a bad slump in 1984. Last year's rating held the 1985 level, except for very poor numbers on the Redskins-Giants game, which ran opposite the seventh game of the World Series.)

Then came Dierdorf, a sportscaster with a Type-A delivery that some viewers thought might overwhelm the soft-spoken Gifford. Instead Gifford's even-keeled analysis seems sharper than ever, and his bursts of humor and insight in tandem with Dierdorf make the telecasts a treat.

It's working out "just fine," said Gifford. "He's a lot of fun to be with and travel with. I like that. In the booth he was comfortable and easy-going from the first pre-season game on. He has a great sense of humor and he's a very sensitive person." The feeling's mutual. Said Dierdorf: "Gifford and Michaels have been super in making me feel welcome. Frank's been more of a help than I have any right to expect."

Gifford is renowned for his loyalty to the NFL; his critics have said he doesn't criticize players. A fairer statement is that he doesn't take cheap shots when a player drops a ball or misses an assignment. Gifford said he feels he's done his job if he points out that that ball "could have been caught."

His love for the game comes through clearly. More than a few times he has cut off aimless banter and clowning in the booth with, "Hey, guys, there's a game going on down there."

Criticism doesn't seem to wound him, either. "I've been criticized since I was a sophomore in high school," he said, "and I've had my share of accolades. In this arena you're going to have critics and you better get used to it. I try to keep myself prepared. I know a hell of a lot about what I'm doing."

When Howard Cosell slashed him in his book I Never Played the Game, Gifford held back. He admitted that he was angry for about five minutes but decided that it was sad that Cosell chose to flail away at those who had made his career possible.

He also feels that too much is often made of the personalities in the booth. For Gifford, it has always been a case of "the game is the thing and everything else, including the sportscasters, is a distant second. We are not more important than the game. We are there to enhance the enjoyment of the viewers. Good games bring good ratings and bad games bring bad ratings. We help a little, but the bottom line is that a good game makes a good show.

"In the early years of 'Monday Night Football,' we were treated like lords and gods as we went from city to city. We were getting keys and parades and luncheons. How many times can you get the keys to a city? That's toned down in recent years, although Monday night is still very special in the stadiums. There's an aura of excitement attached to playing under the lights in an ABC game.

"You know," Gifford recalled, "when it all began, Monday night football was offered to NBC and CBS. They turned it down; ABC took the package because it had nothing else. It sure has been successful. I never even dreamt it could be so successful."

But then Gifford has been attached to success all his life. As tailback and defensive back at the University of Southern California, he was an All-America selection and in 1975 was inducted into the National Football Foundation Hall of Fame for his record performances.

He signed with the New York Giants in 1952 as the team's top draft choice for a salary of $8,000 and a $250 signing bonus, which covered the hospital bill for the birth of his first child. He can also recall crowds as small as 9,000 watching Giants' games in the Polo grounds. Gifford played both as a running back and a cornerback on defense. "I enjoyed playing. I did it for fun. I sure as hell didn't do it for the money."

He said when he first started he expected to play only for a couple of years. He played in the secondary with Tom Landry, who became a player-coach. He recalled a close game in which he slipped out of position and intercepted a pass. As he raced goalward and was about to be caught, he lateraled to Landry, who scored the clinching touchdown. "You know," said Gifford, "when he reviewed the films, Landry gave me hell for being out of position."

A new young coach, an assistant from Red Blaik's staff at West Point, took over the offense: It was Vince Lombardi. Gifford speaks in reverent tones of Lombardi and how he helped turn the Giants into champions before going to Green Bay to become head coach of the Packers.

A collision with Philadelphia's Chuck Bednarik put Gifford on the shelf for a year. He might well have retired, but he came back a year later in 1962, became a flanker instead of a running back, and played for three more years.

He made All-Pro six times, was the NFL's Most Valuable Player in 1956, when the Giants won the title, and was the MVP of the Pro Bowl in 1959. In 1964 the Catholic Youth Organization named him Sportsman of the Year. His Giant records -- 5,434 yards receiving, 484 points and 78 touchdowns -- still stand.

Gifford has been honored in broadcasting too. In 1984 he received the Christopher Award for his coverage of the 1983 Special Olympics on "Wide World of Sports." He has been chairman of the Special Olympics sportscasting committee since 1974 and a member of the Special Olympics board of directors since 1983. Three years ago the Multiple Sclerosis Society of New York honored him with its Founders Award, which included a $100,000 research grant in his name. He has also authored several books, including Gifford on Courage, which profiles 10 of the most courageous athletes he knows.

His long-time ties with the Special Olympics go back to 1968 when Eunice Shriver asked him to round up prominent athletes for a meeting in Chicago. "Everyone I called showed up and I've been helping ever since. I'm very proud of my association with the Special Olympics." Along the way his daughter Vicki married Michael Kennedy, son of Bobby and Ethel. In October, Gifford was presented with two granddaughters: Rory Gifford Kennedy, the third child of Vicki and Michael Kennedy, and Christiana Francine, second child of Gifford's son Jeff and his wife, Caryn. Gifford also is the father of Kyle.

How can a five-time grandfather of 57 continue to look as though 40 is still around the corner? "In my mind, 40 is still around the corner. I take good care of myself; I maintain a good mental frame of mind, have a wonderful wife and lead a very happy life."

Football occupies Gifford, but it does not consume him. "It's not my life. It's a game." He reads five newspapers a day and doesn't start with the sports pages.

He still considers Franz Klammer's downhill run for a gold medal at Innsbruck in 1976 as his most exciting moment in sports. "He was only 21 years old," he recalled. "It would still be No. 1 even if I wasn't involved in the call of it. I've got an Emmy on the shelf for that one."