Third ranked Duke, an inconsistent, tentative team a year ago, became the aggressive, confident club again tonight that finished second in the country in 1978 and whipped sixth-ranked North Carolina, 86-74, to win the Big Four basketball tournament.

Led by Eugene Banks' 22 points and tournament MVP Mike Gminski's 21, the Blue Devils put on a virtuoso second-half performance, blowing to a 16-point lead with 4:35 to play and coasting to victory. Duke's other starters also scored in double figures, Bob Bender, Kenny Dennard and Vince Taylor scoring 13 points apiece, with Bender adding seven assists.

"That's the best Duke team I've ever seen," Carolina Coach Dean Smith said. "If they play like that during the nationals, they'll win it, the championship."

While Duke played a solid offensive game, shooting 63 percent, it was the defense that was the difference in this game.

"We've worked awfully hard on that man-to-man," Duke Coach Bill Foster said. "It's nice to see that work pay off.'

Specifically, Duke worked extremely hard in preseason on its man-to-man defense after being almost exclusively a zone team the last two years.

Tonight, the Blue Devils played man-to-man for 30 minutes and the Tar Heels, normally calm in their shot selection, shot 46 percent.

"We were ready for their man-to-man," Tar Heel guard Al Wood said. "We knew they had used it the first two games and we expected it. But we didn't handle it."

Wood, with 19 points, and Mike O'Koren, with 25, were the only Tar Heels who played effectively.

Still, the game was close for 33 minutes, largely because of Carolina's aggressive defense and Duke's poor foul shooting (eight of 17 at one point).

But with the score 57-53 and the game apparently headed for a typically tight ACC finish, the Blue Devils began working the defensive board aggressively, running their transition offense perfectly and passing with aplomb. A 14-2 streak put the game away for Duke.

Dennard applied the coup de grace with a slam dunk off a pass from Gminski with 4:35 left and the only thing that remained undecided was the final margin.

"We knew what we had to do, play aggresive," said Gminski, frequently criticized in the past for not being aggressive. "You have to fight fire with fire and that's what we did tonight. We knew we had to stay on them all the time."

Gminski was a tower of strength during the two-night tournament, winning the MVP award for the second straight year. He had 48 points, 28 rebounds and 12 blocked shots while playing 77 of a possible 80 minutes in the tourney.

Most satisfying for Foster, however, was the play of his junior forwards, Banks and Dennar. Fabulous freshmen during Duke's Cinderella rise two years ago, they were scared sophomores a year ago.

Tonight, they were their old selves, rebounding, passing beautifully and shooting confidentally to give Gminski all the support he needed.

And added bonus for Foster was the fact that this was his 300th win as a head coach and it came against archrival Smith.

"I forgot about winning 300 10 years ago when I had about 286," Foster cracked.

He could afford the joke because although as he put it "one game does not a season make," this one made it apparent his club, 3-0, will be heard from all season.

North Carolina State defeated Wake Forest in the consolation game, 70-65.