Donald Joseph Dovey, a computer programmer and avid cross-country skier, hiker and mountain climber, died Sunday on a ski outing in the backcountry east of Crystal Mountain Ski Area. A midday avalanche, unleashed with no warning but the deafening crack before its thunderous 300-foot plunge, buried Dovey upside-down beneath 500 feet of snow. He would have turned 38 next month.Dovey had joined six other cross-country skiers on a backcountry ski trip organized by The Mountaineers, a Seattle-based recreation club with 15,000 members and a strong safety record. They were skiing below East Peak, above the ski area, when the 120-foot-wide, 300-foot-long avalanche dropped into the Cement Basin of Norse Peak Wilderness area. The area is part of the Mount Baker-Snoqualmie National Forest, and outside the ski area boundaries, but the group needed no permit and were doing nothing illegal, authorities said. Relatives, ski area officials and law enforcement authorities credited the heroism of several others for trying to save Dovey, including a 69-year-old physician who tried to resuscitate him and one man who, after witnessing the avalanche from an upper ridge, skied down to Dovey, then climbed several thousand vertical feet back up to the ridge to return to the ski resort for help. Neither of the men was identified yesterday.