For the past two years, Mike Dombeck, the chief of the United States Forest Service, has strug-gled to change the culture of a notoriously stubborn agency that has long favored the harvesting of timber in the national forests at the expense of wildlife protection and other environmental values. But old habits die hard at the Forest Service, no matter who is in charge. That is the unhappy subtext of Federal District Judge William Dwyer's recent ruling that the Forest Service has been violating a landmark 1994 plan to protect the spot-ted owl in the old-growth forests of the Pacific Northwest, mainly by failing to conduct wildlife surveys on Federal land before approving logging contracts. The decision, which also faulted the Bu-reau of Land Management, could halt logging on more than a half-million acres of Federal land.