he San Francisco 49ers defeated the Cincinnati Bengals, 26-21, today to complete a three-year journey from ineptitude to glory. Not even the fury of a second-half Cincinnati rally could prevent them from becoming perhaps the most improbable Super Bowl champion in history.

This was a moment the 49ers had been waiting 36 frustrating years to celebrate. Now they have a victory they can talk about for seasons to come, a triumph that produced the kind of drama and excitement that has been missing from so many other National Football League championship games.

Never has a team been 2-14 one season, 6-10 the next and the Super Bowl winner the third. But the 49ers have been accomplishing unlikely things all season, and they continued today as they won their first league title.

They built the biggest halftime lead in Super Bowl history, 20-0. Then they almost made more history by blowing it before deflating the Bengals' comeback by stopping 249-pound Pete Johnson on a fourth down at the one late in the third quartr.

But despite that defensive gem, this day still belonged to the offensive genius of Coach Bill Walsh and his quarterback, Joe Montana, the third-round 1979 draft choice out of Notre Dame who now can add the game's most valuable player award to his trophy case.

It was their showing in the first half--Walsh's play calling and Montana's execution--that provided the 49ers with the cushion they needed to hold off Cincinnati. And it was their combined talents during a fourth-quarter drive, setting up Ray Wersching's fourth field goal--tying a 14-year Super Bowl record--that finally ended the Bengals' comeback hopes.

"This was one rare moment when a team without great stars and experience raises up," said Walsh, who spent 22 years waiting for a head coaching opportunity in the NFL and then won the Super Bowl XVI three years later. "No one could take us. It was the highlilght of my life. Anything can happen now."

Cincinnati will wonder about its four turnovers, including two that wiped out potential scoring opportunities. The Bengals will wonder about that Johnson goal-line run. It was a play that had worked so many times before in the season (Johnson rushed for 12 touchdowns) but not today, not when Cincinnati needed it the most. And the Bengals will wonder about their dreadfully flat first-half performance.

"It was just beginning to look like one of those days," cornerback Louis Breeden said. "We couldn't do anything right, but we came out in the second half and we had a shot. Nobody wanted to be embarrassed and I don't think we were."

Yet why were the more experienced Bengals seemingly much tighter than the 49ers, a team that began this season with 20 new players? "We were loose in the locker room before the game, but for some reason, we were tense when we first came out on the field," said tight end Dan Ross, who caught a game-record 11 passes. "Stage fright, maybe."

Montana, in only his third pro season, and Walsh, the former Bengal offensive coordinator who was denied the team's head coaching position, had just as much reason to be jittery. But they were as steady as Starr and Lombardi at their best.

In a first half that could be used as an offensive training film, Montana completed 12 of 18 passes for 132 yards and one touchdown. He turned Walsh's don't-be-greedy calls into time-consuming scoring drives of 68, 92 (longest ever for a Super Bowl) and 61 yards to frustrate the Bengals.

And then when Cincinnati's Archie Griffin, the two-time Heisman Trophy winner turned fill-in pro player, fumbled away a squibbed kickoff at the Bengal four and Wersching kicked a 26-yard field goal with two seconds left in the half, the game seemed all but over.

But a defensive adjustment by Cincinnati at halftime changed the Bengals' outlook dramatically. They decided to revitalize themselves by turning to an all-out blitz on almost every play.

Suddenly, Cincinnati forgot about two devastating first-half mistakes: a Ken Anderson interception at the San Francisco five after the Bengals had recovered a fumble on the game-opening kickoff, and a fumble by receiver Cris Collinsworth at the eight.

Quarterback Anderson, once a Walsh protege, had been just off-target in that first half, missing open receivers by inches while trying to avoid the pressure of the 49er defensive rush. He was being clearly outplayed by his younger counterpart in the San Francisco uniform.

Now Anderson was a different man. He took the Bengals on an 83-yard touchdown march on the opening series of the third quarter, scoring himself on a five-yard scramble up the middle. No longer was Cincinnati playing like a team which was outgained, 208-99, in the first half.

Walsh decided to counter the Bengal blitzing by turning to running plays. The result was almost disastrous. San Francisco could gain only four yards in the period after trying only two passes. Cincinnati kept pounding and pounding, hoping for a breakthrough.

It almost came midway through the quarter. A stunning 49-yard Anderson completion to a speeding Collinsworth on a third and 23 play gave the Bengals a first down at the 49er 14. On a fourth and one at the five, Johnson bulled for a first down, helped by San Francisco having only 10 men on the field.

But that would be the 49ers' last mistake in this dramatic sequence. Johnson, who has made a living producing in these situations, got to the one. On second down, linebacker Hacksaw Reynolds slashed into the fullback, stopping him for no gain. On third down, an Anderson pass to halfback Charles Alexander in the right flat was stopped inches short of the end zone on a memorable open-field tackle by Dan Bunz. On fourth down after a timeout, Johnson tried right tackle. The 49er defense overpowered the Bengal offensive line and Johnson never had a chance. No gain.

"We ran the same play a lot of times," Johnson said. "It's just one of those things that happens. I figured I could go under them. It just didn't work."

Even though Cincinnati refused to fold even after that letdown, the 49ers had the break they needed to regain their poise. When the Bengals finally did get their second touchdown on a four-yard pass from Anderson to Ross with 10:06 left in the game, San Francisco was able to respond with a back-breaking field goal.

To set up Wersching's 40-yard success, Montana first had to complete a 22-yard pass from his own 22 to receiver Mike Wilson for his team's first substantial gain of the half. Then the 49ers started offsetting the Bengal blitzing by calling trap running plays. Seven rushes later, Wersching gave San Francisco a 23-14 lead with 3:25 remaining, making another field goal and Anderson's second scoring pass to Ross incidental.

"In the huddle, we said, 'Let's think this is the last 10 minutes of our life,' " receiver Dwight Clark said about the pivotal 49er drive. "There was also mention of a $9,000 drive (difference in the winning and losing shares). Money is a big motivator in this type of situation."

Anderson had been magnificent in defeat, completing 17 of 20 passes after intermission for 217 yards. His 25-of-34 day set Super Bowl records for most completions and highest passing percentage. But this was also the first time that a Super Bowl loser has ever outgained the winner (356-275).

Walsh had confused Cincinnati by using an unbalanced line in the first half and he had almost broken the Bengals' defensive confidence with the ease in which his team had moved the ball. But his decision to be careful in the third period had almost neutralized his handiwork.

"We didn't know what to expect from them offensively because of Walsh, especially with two weeks to prepare for us," Cincinnati linebacker Reggie Williams said. "They just ran the ball better on us than we anticipated."

Inside the 49er dressing room, the San Francisco players still were trying to believe that this long-sought championship finally was theirs. The veterans, the ones who had suffered through the lean years, probably were the happiest.

"I don't know how we are ever going to top this," tackle Keith Fahnhorst said. "I'm still numb. To grasp something like this, well it's unbelievable."