Montgomery County School Superintendent Wilmer S. Cody proposed yesterday that students and staff members with AIDS be allowed to remain in the classroom in most instances.

The proposed policy is radically different from an interim policy Cody put into effect in October after school officials discovered two Montgomery County teachers had died of aquired immune deficiency syndrome in the previous 13 months.

Under Cody's interim policy, students with AIDS were to be placed on home instruction and staff members in nonclassroom settings.

But a draft of Cody's proposal for a final policy, presented to Board of Education members yesterday, says that only students who are preschoolers, lack control of their bodily secretions, are prone to biting or have uncoverable lesions will be automatically excluded from the classroom. Cody would make the decisions on a case-by-case basis.

Cody said he changed his mind on excluding from school all students and school employes with AIDS after listening to several experts say that AIDS is transmitted only in limited ways and mainly through sexual contact.

The school board is expected to take up the policy at a meeting in January.

Cody's policy is closely patterned after proposed guidelines on AIDS released by the state's Department of Health and Mental Hygiene.

In other action, the Board of Education elected James E. Cronin, a 44-year-old associate professor at Montgomery College in Rockville, as its new president. Cronin, who had been active in county human relations activities before he was elected to the board in 1982, succeeds Robert Shoenberg.

The board selected as its vice president Jeremiah Floyd, 53, a former math teacher who is associate executive director of the National School Boards Association. Floyd was appointed to the board last year to fill a vacancy.