Joe Namath wasn't shy 17 years ago when he brashly predicted a New York Jets victory over the heavily favored Baltimore Colts in Super Bowl III, and he's not bashful today as the new million-dollar baby in ABC's "Monday Night Football" broadcasting booth:

This week he joins Frank Gifford and O.J. Simpson for the NFL season opener between the Washington Redskins and the Dallas Cowboys at Texas Stadium. And Namath is ready to send a bullet right down the middle: " 'Monday Night Football' people are in for a treat. Honest to God, I'm eager."

With three preseason games under his new ABC blazer, he predicts his first season with Frank Gifford and O.J. Simpson "is gonna be good. The more I find out about what they want, the more I can contribute. Because, you know, I'm flexible."

Then, since a 42-year-old married man can be a little more conservative than Broadway Joe of the Jets, he added: "Of course, I have to remind the folks that if we have a real bad game, you just can't help that."

But Namath has no fear of the critics.

"Regardless of what any one of us does, we can't please everybody. I say we'll be very good. I'm excited about it. I'm happy about it and I've convinced myself I have what it takes. The combination of Frank and O.J. gives us a very authoritative group (all three are in the Pro Football Hall of Fame). Right now I'm doing things I feel comfortable with. We'll do more and inject some humor when I'm more at ease."

There are signs that viewers too may be enthusiastic about the new ABC lineup. Or at least curious. The recent Bears- Cowboys contest received the highest rating for an ABC preseason game since 1979. "I think some people have tuned in out of curiosity to see how Joe Namath and O.J. Simpson are doing," said "Monday Night Football" producer Bob Goodrich. "And they've stayed."

For Namath, the audibles called by the production quarterbacks are one of the discomforts of the job. "I have to get used to the mechanics. It's not easy to talk on national TV when four guys are talking into your headset. Then when you're in the middle of analyzing a play, you hear, 'We're breaking away in five, four, three . . . ' Now you have three seconds to end what you're saying. And, although you may have had a good point to make, it doesn't come out so hot."

Namath admitted that he hadn't known "what it would be like in the booth." But director Chet Forte, who has been with "Monday Night Football" since it began 15 years ago, gives Namath top grades at this point.

He recalled that after Don Meredith's first preseason experience, the former Cowboy quarterback was so frustrated he wanted to quit, but ABC sports executives talked him into working out his problems. Then came Fred Williamson, Alex Karras, Fran Tarkington and Meredith's second stint.

"He's at the top of the class," said Forte of Namath. "Joe is going to be terrific. He projects very well. He knows the game. He gets involved and excited. He even roots. He's going to help us in the ratings." (Ratings for "Monday Night Football" were down last year.)

Forte said he's also noted that Namath has a large following. ABC's preseason ratings were the best in five years and it has "a lot to do with Namath. Even youngsters who have never seen him play are lined up for autographs before and after a game. His appeal is still there. He knows how important it is. You don't have to give him a pep talk. He takes it all very seriously," Forte adds.

Namath's wife, Deborah, says that when they watch games he is free with his opinions. She wondered why he didn't go into broadcasting. "He had been doing color for me for two years," she said. "When we watched games, blood would rush to his face." It wasn't long before Namath's agent was talking with ABC about the vacancy created by Meredith's retirement.

A couple of months ago ABC announced that it had signed the former pantyhose-peddling hulk for $1 milllion a year for five years. Namath amended that. "It's for two years," he said, "and ABC has an option after that for the other three years or it can tell me to take a walk."

Namath believes that acting in five movies, a brief TV series ("Waverly Wonders"), and his many TV guest appearances have helped him prepare for this job. But he says his roles in nine stage productions were the most helpful.

"Going out there performing and believing each line in the script," said Namath, reflecting on the experience. "We're all different each day. So is the audience. It not only did wonders for my nervous system, but it also developed my timing."

Namath has played major roles in stage productions of "Picnic," "Little Abner," "Guys and Dolls," "The Rainmaker," "Cactus Flower," "The Caine Mutiny," "Sugar," "Damn Yankees" and "Bells Are Ringing."

In addition to his show business career, he is proud of his knowledge of football. Since signing the ABC contract he has spent time with old coaching friends studying the game and its changes since he played.

"I know what I'm talking about. As a quarterback, I know what linemen are trying to accomplish. I am also able to talk with players and coaches before the game, and they give me insights that I feel I can pass along to the fans. I have a good knowledge of the game. And I'll rely on that without guessing."

Namath can also bring a second view to the fan. In one game, the NFL's experimental replay camera (tested in preseason only) was used to review a controversial play. Gifford said, "I hope it never comes to this." Simpson concurred. When the replay showed the officials were wrong and the bad call was reversed, Namath bellowed, "Hey, I love this."

In the very first minutes of his initial telecast, after Simpson had disgreed with him, Namath shot back, "You ran with your eyes closed most of your career."

Still, Simpson says he likes working with Namath. "We mesh well, because we both played the game at the same time and we've been friends."

Namath's biggest problem of this season may come during the Dolphins-Jets game on Oct. 14. That's the day the Namaths' first child is scheduled to arrive. "Debbie travels with me wherever I go. We have homes in California and Florida and are looking for an apartment in New York. I would like to be there when the baby comes. She'd like me to be there, too. I think we'll get lucky."

He says they've already chosen the child's name: "John Jeffery after my dad and my wife's brother, if it's a boy, and Jessica Grace, because it's pretty and sounds nice, if it's a girl.".

Meanwhile, Namath begins his new career on the heels of several others whose faults the critics made clear after their depatures. Cosell was Cosell (and as yet he hasn't called to offer Namath any advice). Tarkenton contested too much. Meredith was lovable but found it difficult to foil with nice guy O.J., something he did well with "Black Hat" Howard. Williamson and Karras did not stay long and received generally low grades all around.

Namath's strong points will be best evaluated as the season progresses. One thing is certain: He isn't bringing in any of the warts of his predecessors.