About 150 people rallied yesterday in Central Park to call for a ban on vehicular traffic on the 6.1-mile main loop, which includes the East and West Drives, at all times this summer. Currently, traffic is permitted there on weekdays from 7 to 10 a.m. and 3 to 7 p.m. Transportation Alternatives, a nonprofit group for pedestrians and cyclists that organized the rally, announced that six members of the City Council whose districts adjoin the park favored an experimental summer-long ban. The group also said it had collected 100,000 signatures in support of a year-round ban. Neither proposal would affect the Central Park transverses, which are open to traffic at all times.