Yellowstone, N.P. – Snowmobiles could continue using Yellowstone and Grand Teton National Parks for at least the tnext three winters under a federal proposal to be released Thursday. The plan by the Naitonal Park Service is meant to buy time until a more permanent solution to snowmobiling use at those parks can be found. A Yellowstone spokesman says the agency is trying to come up with an appropriate plan for up to three winters. The aim is to allow people to know what to expect and allow the Park Service some time to gather more information. But he says the plan calls for strictly limited snowmobile and snow coach use.