Bjorn Borg withstood any aggressive wask, the fiercely partisan Roman crowd, and some of Adriano Panatta's most thoughtful tactics to win the Italian Open tennis championship yesterday for the second time.

After nearly walking off in the final set because a few spectators in the crowd of 9,000 that jammed the stadium at Foro Italico were throwing coins on the court, Borg summoned some of his peerless passing shots to defeat Romeos dashing tennis idol, 1-6, 6-3, 6-1, 4-6, 6-3, in a three-hour match of uneven quality but sustained interest and excitement.

"I think because of the crowds, this is maybe one of the most difficult tournaments in the world to win," said Borg, the first No. 1 seed to triumph there since Rod Laver in 1962.

Borg, already the owner of two French (1974-75) and two Wimbledon (1976-77) titles, was the youngest champion in the history of this second most important clay court tournament of Europe when he won at age 17 in 1974. His second victory yesterday came nine days shy of his 23rd birthday.

The white marble "Campo Cenrale" (center court) was jammed to the top of the new bleachers that were erected last fall, increasing the seating capacity but unfortunately eclipsing the view of the 17 massive status in various athletic poses that surround the groundiose arena. They used to peer over the top of the stands, their stony expressions imparting a sense of antiquity to the protracted struggles on the slow red clay of the Eternal City.

The sunbaked crowd, forming a patchwork of blazing colors in their spring fashions and splendid variety of hats, chanted and cheered noisily for Panatta, as is their custom. But there was little of the unruly behavior that provoked Spaniard Jose Higueras into defaulting his semifinal match against Panatta at one set all on Saturday.

The only brief interruptions in play came in the eight game of the fourth set and the third game of the fifth, when a few Roman spectators did as visitors to the city do at the Trevi Fountain, threw coins. But they threw them at Borg.

This momentarily pierced the stolid Swede's usually ironclad concentration. He was clearly annoyed, complained to the referee, and walked over to talk to his coach, Lennart Bergelin, in the courtside marquee.

"I told him, if they do this three or four more times, I might retire," Borg said later. "Up to that time the crowd had been very good, no problems, but this throwing coins is very irritating. One hit me in the leg . . . It is distracting and dangerous."

After the last incident, as Borg was about to serve in the fourth game of the final set, the umpire sternly said to the crowd: "Let us finish the final. These are unsporting gestures." He was loudly applauded, and there was no further trouble, as already heavy security forces in the stands were increased.

Borg also did his part to defuse any riotous inclinations the crowd might have had by giving too.

A 6-foot-2 attacker who had won the Italian and French opens in 1976, Panatta has the type of aggressive all-court game that can trouble Borg. He had won six of their previous meetings.

In the first set, Borg looked stiff and sluggish. Panatta was sharp and playing intelligently, bringing Borg to the net with perfect drop shots, feeding him soft balls ans short angles.

The crowd erupted as Panatta broke serve with a backhand down-the-line pass in the first game, then groaned en masse as Borg broke right back. Panatta broke again in the third game with the help of a wasp that tried to attack Borg at 15-40.

The young swede dodged the bee, doing a reasonable facsimile of the Watusi as it buzzed about his head and shoulders, and swiped at it with his recket. Instead, he hit himself just above the left eye and had to have a resultant cut patched.

Back on court, Borg netted a forehand drop volley to lose his serve, and Panatta was off on a six-game binge, to 1-10 in the second set.

But the unflappable Swede, who had gotten only eight of 21 first serves in court during the first set, held serve for the first time to make it 1-1, Panatta committing four unforced errors after Borg got four first deliveries in. That signaled a turning point.

Panatta lost his serve in the next game on his first double fault. He was losing his touch as Borg was finding his.

To the dismay of his doting legions, Panatta became uncertain and ragged on his ground strokes.

His second serves grew shorter, and he forgot the tactics that had worked so well in the first set. Instead of drop shooting, he tried to hit deep approaches, giving Borg a target and pace for his passing shots.

Panatta did get back from 1-4 to 3-4 in the second set, and might have taken control if he could have broken Borg in the eighth game. He got to 0-15 by suddenly remembering the drop shot, but then Borg slammed the door, serving four strong points including his first ace. He broke the dispirited Panatta for the set, won 10 of the next 14 points, and ran out the third set in 26 minutes.

Panatta is a bold fighter, though. After the 15-minute intermission he started playing the way he had in the first set: Serving better, getting to the net for agile, lunging volleys, and again using to great advantage the drop shot he disguises so well.

Attacking Borg's second serves, getting to the net as often as possible for razor-edged volleys, Panatta broke in the fourth and sixth games to lead 5-1. The crowd came alive, chanting and applauding him rhythmically: "Ad-ria-no," clap-clap.

Panatta had three set points at 5-1, 40-0 on his serve, then inexplicably collapsed as Borg pulled back to 4-5, 30-30 on his. But a Borg backhand error brought Panatta to set point for the fourth time, and he grasped it with a backhand down-the-line passing shot on the sideline.

Panatta did not know if the ball caught the line or not - the linesman made no call - but Borg signaled that it was good and the crowd let out a delayed roar of approval.

In the fifth set they went - the first time a men's final had gone the distance here since 1969 - and Borg broke in the first game, Panatta netting a forehand volley off a mis-hit backhand return at 30-40, then held his serve at love.

The coin-tossing episode nearly ruined his final charge, but Borg regathered his concentration and produced his best tennis of the match, holding serve at 15 in the fourth game, at 30 in the sixth, and at love in the eighth win four spectacular backhand cross-courts, one that forced a volley error and three for clean passes.

That got him to 5-3, and Panatta looked exhausted, drained. He saved one match point on his serve in the ninth game, had five game points, but was broken for the set after six deuces, double-faulting for the sixth time and then netting a backhand volley on the final two points.

Borg earned $23,000, plus the respectful and enthusiastic applause of the crowd.

Panatta collected $12,500 and a standing ovation for having reached the final unseeded - with a little help from is friends.