Who can say what happened to the Cleveland Browns in the second half of today's AFC semifinal playoff game with the Miami Dolphins?

After a heroic performance in the first 30 minutes put them ahead, 14-3, and a quick-hitting touchdown drive gave them a 21-3 start with less than four minutes gone from the third-quarter clock, Coach Marty Schottenheimer's squad played as if in dire need of a plug from a high-voltage cattle shock. Failing that, they lost, 24-21.

They played as if everything everybody ever said about their back-door, 8-8 season were true; as if the 12-4 Dolphins would eat them up like chickens picking off star-struck June bugs on the back porch.

Something else: who can say what happened to the Dolphins in the first half? Or explain their total lack of defense against the run, their uncertain passing game and their self-defeating attitude of roll over and play possum?

Some things that die truly can live again, including the Miami Dolphins today before 75,128 at the Orange Bowl. Quarterback Dan Marino made up for a so-so start and played brilliantly in the stretch. He ended up with 25 completions on 45 attempts for 238 yards and one touchdown. For the Browns, former University of Miami quarterback Bernie Kosar's return to the place that helped make him famous could have been better. He was good on 10 of 19 passes for 66 yards and one touchdown.

Said Dolphins Coach Don Shula: "It seems the tougher the situation, the better we play. It was rough going, but it seems there aren't too many times when these guys weren't able to get it done."

Even the very beginning of this nationally televised game was deceiving. After fullback Woody Bennett found a hole and rambled 17 yards for the Dolphins, and Marino threw seven more to tight end Dan Johnson to put the offense in Cleveland territory, one might have predicted an ugly rout. But like so many other first-half Miami drives, this one died. Fuad Reveiz came out and kicked it good from 51 yards, lifting the Dolphins to a 3-0 lead with 10:34 remaining in the first quarter.

Luckily for the Browns, their two big running backs came into the game with hearts beating like thunder and proceeded to show why they had become only the third tandem of ball carriers to gain over 1,000 yards each in a single season. Kevin Mack and Earnest Byner were most effective taking quick pitches straight into the flexed muscle of the Miami defensive front. Curtis Dickey also had runs of 10 and nine yards to add to the effort. But it was a 16-yard pass from Kosar to tight end Ozzie Newsome that gave the Browns a 7-3 lead with 1:24 left in the first quarter. Newsome had worked his way behind the coverage of linebacker Alex Moyer.

Later in the half, Kosar was less perfect passing to receiver Brian Brennan and threw into the hands of cornerback Paul Lankford at the Cleveland 25. Marino completed passes of six and 10 yards to running back Tony Nathan and one of two yards to Bruce Hardy in moving down to the seven. He then looked for Mark Clayton in the end zone but was intercepted by safety Don Rogers, who returned the ball 45 yards and helped set up the Browns' second touchdown of the first half.

"On that interception," Clayton said, "somebody was all over my back. I don't know what the refs were looking at all day but it wasn't what was happening on the field."

Byner, who led the Browns' rushing game with 161 yards, busted through for 21 yards and a touchdown on a third-and-eight with 58 seconds left in the second quarter, giving his team a 14-3 lead.

"We were having plenty of problems stopping the run," Miami defensive end Mack Moore said. "At half, we worked on it and came back strong. We had to change the line around a little bit to make things right."

Mike Charles, the Dolphins' nose tackle, said, "I played it more straight up in the second half. I got right up on the center. In the first half, I was moving from one side to the other, playing it offset. It just wasn't working. They were blowing right through there."

At the end of the first half, Byner had 60 yards, Mack had 50 and Dickey had 31. The leading Miami rusher was Bennett, who had managed to gain 15 yards.

Said Marino: "We were behind, but we just knew we had a lot of time. There was no need to rush and try to get it all back at once."

The first time the Browns got the ball in the second half, Miami linebacker Jay Brophy came up with two devastating hits to running backs Mack and Byner as they approached the line of scrimmage. It appeared the Dolphins had made the necessary adjustments at halftime and now would exploit the Browns' young offensive backfield. But a few plays later, Byner broke through a canyon of a hole and ran for 66 yards and the touchdown with 11:22 to go in the third period. To give him room in which to maneuver, Clarence Weathers cleared out two defenders with a single block. Byner made it 21-3 by accelerating past a number of straggling defenders.

Dolphins linebacker Hugh Green said: "I think the Browns' running game was the best we've faced this year -- they have a solid one-two punch. We just sat on the sidelines calmly trying to correct things. Everyone felt very confident that our offense could bring us back. The key was getting them the ball and letting them do their magic."

The magic started the next time the Dolphins got the ball. Marino drove the team 74 yards in 13 plays, passing to tight ends Hardy and Johnson, and to Nathan, who made 10 catches for 101 yards. But Marino passed six yards to receiver Nat Moore for the touchdown. The Browns led, 21-10, with a little more than five minutes left in the third quarter.

"I think in the second half Marino realized his wide receivers were taken away," defensive back Hanford Dixon said. "He started going to his check men -- the running backs and the tight ends. All you can do is run up and make the tackle, but it's still a six-yard gain."

Marino was just as sharp on the Dolphins' next possession, taking advantage of a 26-yard punt by Jeff Gossett that gave Miami the ball on the Cleveland 49. To score, rookie fullback Ron Davenport decked Rogers after clearing the front line and broke loose for 31 yards and the touchdown with 1:41 left in the fourth quarter. The Dolphins still trailed, 21-17.

"I just knew somebody would catch me once I got into the open," Davenport said. "I was just worried somebody would run me down and tackle me from behind."

Davenport moved the Dolphins ahead, 24-21, on a one-yard run with just under two minutes remaining. His burst up the middle completed a drive that covered 73 yards in nine plays. Davenport said he knew he had to score because his teammates were out there blowing people off the ball, trying to make it easy for him, Miami's designated scorer with 13 regular-season touchdowns.

"In the huddle," he said, "they told me I would be the one to put it in. They told me in the huddle the hole would be there. I told them what they knew. I said just give me the ball, give me a hole, and I'll score for you. I knew we could do it."