I wrote to Ron Wyden (and other congress critters), and received an interesting response from his office today. I'm assuming you know this information, but if not, I post it here (this is a quote from the letter-any typos are my fault):
Regarding the use of chainsaws or other mechanized tools for trail maintenance in designated wilderness areas, the Wilderness Act of 1964 as amended allows for the use of such tools under some limited circumstances. In situations in which the wilderness manager finds that the minimum tool that will suffice for a necessary action extends beyond the primitive tool requirements of the Wilderness Act, the manager may, following the United States Forest Service Minimum Requirement Decision Guide (MRDG), be granted an exception from the primitive tool requirement. This process has been utilized to permit the use of power tools, helicopters, fire and the construction of shelters as necessary for maintenance and other essential wilderness restoration or harm mitigation actions. I encourage you to visit
http://www.wilderness.net/index.cfm?fuse=MRDG for a detailed description of the MRDG process.
So, with the correct approval, it sounds like using chain saws is a possibility.....But it would take a little work and justification. I would think that an acceptable compromise would be allowing chain saws in wilderness areas every 3 years or so to clean up the damage caused in the preceding years. There is at least one sample on the above website that talks about reconstructing a trail after fire damage, but many of the arguments could be used for trail maintenance as well.
Link on FS guidleines:
http://www.wilderness.net/MRDG/documents/MRDG_FWS_wilderness_policy.docLink on trail reconstruction:
http://www.wilderness.net/MRDG/documents/trail%20reconst_fire-structures-hel.docLink on another trail reconstruction request:
http://www.wilderness.net/MRDG/documents/trail_reconst_rock_%20drill.docInteresting....