The period for public comment on proposals for sweeping changes at Rainbow Bridge National Monument has been extended 30 days until Dec. 20.

Monument Superintendent John Lancaster, based in Page, Ariz., said copies of the General Management Plan, environmental assessment and other plans can be obtained by writing to him at P.O. 1507, Page, AZ 85040, or by telephoning (602) 645-2471.The plan proposes a two-phase approach to management at the monument, including construction of a seasonal contact station at Forbidding Canyon, in the water approach to the monument from Lake Powell. Entrance fees would be collected; the number of hikers around the natural bridge would be limited; and National Park Service interpreters would serve on concessionaire-operated tour boats.

The second phase would inaugurate a shuttle transportation system during the monument's busiest period.

Meanwhile, the National Parks and Conservation Association is lambasting the plan, saying the proposal fails to address the primary problem at the bridge - overcrowding. The present situation creates "a carnival atmosphere that degrades the site," says the NPCA in a nationwide call for letters to the Park Service.

The group charged that the Park Service takes a "how many people can you fit in a phone booth" approach to setting carrying capacity.

The level that the Park Service feels is the monument's capacity, 390 people at a time, adds up to about 655,200 visitors per year - a 300 percent increase over current numbers, said the association.