Al Gore, acknowledging that he has serious competition for the Democratic presidential nomination, said yesterday that he wants to debate Bill Bradley on environmental issues, among other topics. Most mainstream environmental groups are not ready to pull their support from Gore, as Friends of the Earth did when it endorsed Bill Bradley earlier this month, but groups also have not made up their minds to back him. Gore may anger some enviros with his support of timber cutting in New Hampshire’s White Mountains National Forest, a stance popular with some of the state’s residents.