When the City Council convened Monday after about a month's recess, everyone expected a hot debate to develop on the new Harvard Square traffic plan. But oddly enough, there was not even a mention of it.

Instead, the councillors attacked other heavy traffic--not drugs, not underground publications, not rats. But hippies. Harvard's hippies at Holyoke Center.

The Council rarely plays the role of guardian to Harvard, but that's what it decided to do this week. Councillor Walter J. Sullivan presented a motion to ask City officials to seek ways to eliminate the congregation of "undesirable persons" in and around Holyoke Center.

Sullivan's order was adopted. It also asked the City Manager to confer with Harvard to seek adequate 24-hour supervision of this area in order to prevent it from becoming "a haven for undesirable persons, thereby destroying the purpose for which this beautiful area was constructed."

The order has not yet gone into effect, for undesirables were still roaming around the grass pasture yesterday.