The Sierra Club yesterday began delivering 600,000 postcards to Congress and President Clinton urging them to protect giant sequoias in California, trees that can live up to 3,000 years and grow to 100 feet around at the base. Many of the remaining sequoias are within national parks, but enviros are pushing for additional protections for sequoias outside park boundaries, saying that off-road vehicles and logging of other tree species should be banned in the vicinity of the sequoias. Clinton last month asked the Agriculture Department for a recommendation on whether he should designate a 400,000-acre Sequoia National Monument to protect many of the giant trees. Yesterday, the House Resources Committee approved a bill that would require 18 months of study before any action could be taken to protect the trees.