The roar of the gallery behind the second green echoed through the chill, damp air at Firestone Country Club at about 2:30 yesterday afternoon, heralding Gil Morgan's eagle at the 500-yard, par-5 hole. The cheers sent a message to Hubert Green as he prepared to sink a 25-foot putt from the fringe of the first green for a one-stroke lead.

The message became all too clear to Green 18 holes later when Morgan won the $300,000 World Series of Golf, Green three-putting for a bogey on the first hole of a sudden-death playoff.

The soft-spoken Morgan, 32, who qualified for this elite 26-man field as a multiple winner on the PGA tour, collected $100,000 and a 10-year exemption from tour qualifying as well as the biggest title of his five-year golfing career.

Green and Morgan finished tied after the regulation 72 holes, Green hitting a magnificent five-wood approach and sinking a clutch 15-foot putt for a birdie 3 on the tough 465-yard finishing hole of a Firestone course that played to its full length after torrential rains Saturday night.

Those two brilliant shots seemed to make amends for a sloppy stretch of 10 holes in which Green's normally sure putting touch deserted him, causing him to bogey the eighth, 11th, 12th and 16th holes as his three-stroke lead evaporated.

They had started out challenging each other. Green responding to Morgan's eagle by bridieing the first three holes to go five under par for the tournament. But in the end they took turns giving away the lead.

So did Tom Watson, who birdied five of the first 11 holes to cause a brief three-way tie, then bogeyed the 14th and 15th to fall back. He finished third win 74-70-69-67 - 280, even par for the four rounds.

Having saved par and a tie for the lead with a 10-foot putt on the 15th, then at 18 having gotten back the stroke he dropped by "foolishly" misjudging the wind on his third shot into the "the Monster" 615-yard 16th, Green seemed pumped off as they headed back to the 14th hole to start sudden death.

The slender, 31-year-old Alabaman had a 2-1 record in previous tour playoffs. Morgan, so easygoing that he seems less like an eye doctor than an anesthesiologist who has taken his own medicine, had never been in one.

"I was a little edgy about my chances," said Morgan a longer hitter than Green. "He's a good player, a good putter, and he had experience in playoffs. But 14 was a good hole to start on for me - a pretty tight driving hole."

Both had taken par 4 the first time at the 410-yard hole, which doglegs slightly to the right and has a massive, undulating green guarded by three traps on the left and one on the right.

Green drove first, just into the collar of the right rough, leaving himself 175 yards to go. Morgan was in the left rough, slightly shorter and with a bit deeper lie.

Morgan hit his seven-iron second shot onto the green, but in tough position, 40 feet to the left of the hole. He was worried. "There's so much break in that green it's awesome," he said later.

Green got closer, 25 feet, but was on the back fringe. He had to like his chances of getting down in two putts more than Morgan did his.

Morgan - who had made a couple of spectacular putts earlier, holing a 30-footer over a hump for his eagle on No. 2 and lipping out an 80-foot birdie try on 18 - stroked his putt firmly. It broke left to right and stopped 18 inches from the hole.

Now the pressure was on Green. His first putt, starting out along the fringe, broke much more severly left to right than he had expected. It slipped 4 1/2 feet by on the right.

He studied his second putt. Finally he stroked the ball. It was off line all the way, breaking two inches to the right.

Green must have felt as crestfallen as he did earlier in the year when he missed a three-foot putt on the 72nd hole of Augusta National Golf Club that would have tied him with Gary Player and sent the Masters into a playoff.

"I look at the second putt twice. It looked like it was supposed to be light. I looked at it a couple of more times and it appeared to be straight. I said, 'Well, it's got to be straight,'" a disconsulate but gracious Green said later.

"After I missed it, (Ken) Venturi (1964 U.S. Open champion and an expert commentator for CBS) said everybody's missed that putt to the right. It doesn't look like it breaks. I wish he had said me before I hit it."

Morgan had expected to go to another hole.

"I thought he'd make the putt, I really did. He's a good putter," said the winner after putting his 1 1/2-foot clincher dead in the center of the cup.

Morgan, who benefited from the overnight rain that eliminated long rolls off the tee and made greens much easier to hold than they had been for three rounds, finished regulation play in 72-72-67-68 - 278.

Green, who insisted at the outset that this was not his type of course, but led after the second and third rounds, finished 70-67-71-70.

Green collected $45,000 as runnerup, Watson $19,000 for third place. Defending champion Lanny Wadkins, whose 66 yesterday was the best round of the tournament, finished fourth at 70-73-73-66 - 282 and earned $12,500.

Lee Elder of Washington, D.C., who qualified for the World Series for the first time by winning the Greater Milwaukee Open and Westchester Classic, finished in a tie for 17th place with Bruce Lietzke, Elder shot 74-73-74-70 - 291.