The Cambridge City Council yesterday virtually approved Harvard's $2.8 million plan for a mall between the Yard and the Law School.

In directing the City Solicitor and Harvard attorneys to work out the legal details of the project, the Council twice voted unanimously in favor of the proposal. All that remains now is for the University and the City to sign a number of formal agreements and then for the Council to approve these agreements.

Work on the combination mall-underpass will begin early next spring with the relocation of certain utilities. Actual construction of an underpass under Cambridge St. (in front of Memorial Hall) will start next fall and will probably be completed by the summer of 1967. According to the proposal, the City will close off a section of Kirkland St. (behind Mem Hall), thus allowing the University to build over part of the andoned roadway.

During the construction period, motorists will use two temporary roads to navigate the distance between the Cambridge Fire station and the Littauer Center of Public Administration. One of the detour roads will cut across Memorial Hall's triangular plot and then sweep behind Littauer Center, coming within 15 or 20 ft. of the center's back stairs This road, carrying east to west traffic then curves in front of Gannett House and connects with Mass Ave. The other road, with west to east traffic, comes up from Harvard Square and veers sharply towards Mem Hall and then connects with Broadway.

At yesterday's Council meeting, Harvard representatives showed the effects of their appearance before the Council when they underwent nearly two hours of hostile questioning. L. Gard Wiggins began his testimony to the Council yesterday with the announcement of a small, but significant, retreat.

The reversal involved Summer Rd., a small street two blocks east of Memorial Hall. Under last week's proposal, a large number of vehicles -- including a significant number of trucks, trailers, and busses -- would have been directed down Sumner Road. Sumner would have received the influx of traffic because Quincy St. between Kirkland and Cambridge Streets would have been made one-way. The only convenient way for cars and trucks leaving the underpass to get to Kirkland St. would have been via Sumner Road.

It was this aspect of the plan that provoked the bitterest criticism from the Council. Yesterday Wiggins said that the University has decided to reject this proposal -- the one backed by traffic experts -- and revert to an earlier plan: widening Quincy St. and keeping it two-way. This change also satisfied the Cambridge fire department, which had with-held its approval.

Despite the change, a resident and large property-owner on Sumner Road objected strongly to the Harvard proposal. Norman Swartz pleaded for a two-week postponment on Council action. "We only learned of this last Friday," he declared. His plea was rejected