Twenty-six-year City Council veteran Walter J. Sullivan is set to be selected Cambridge's new mayor tonight, thanks to a key pledge of support from maverick councilor Alfred E. Vellucci last week.

Sullivan, a moderate, and six other incumbent councilors--Thomas Danehy, Francis H. Duehay '55, Saundra Graham, David E. Sullivan, Vellucci and Alice Wolf--along with two rookies, Sheila Russell and William Walsh, will be sworn in today for two-year terms.

The mayor--whose post is largely ceremonial but includes a vote on the School Committee--is selected from among the nine city councillors. Cambridge's council is split between four liberal Cambridge Civic Association members, four more conservative Independents, and the non-aligned Vellucci, who typically sides with the CCA on rent-control and housing issues, which are among the thorniest the council deals with.

Vellucci announced last Monday he will go along with the Independents and back Sullivan, who served as mayor in 1968-9 and 1974-5. Vellucci is slated to be chosen as vice mayor.

Vellucci was considered to be Sullivan's only challenger. Of the three other Independents, Danehy was not interested and Russell and Walsh were both newcomers.

The hottest issue facing the council this year looks to be rent control, which was implemented 15 years ago and currently covers 17,000 of the city's 32,000 rental units.

Noting that last November's election preserved the 5-4 balance in support of the law, Sullivan said in an interview yesterday that "we'll never lose rent control." But he said he hopes to push for some reforms in the law, as well as reforms in laws covering condominium conversion.

Other Development Issues

The other big issues facing the council involve development. Developer Forest City Enterprises wants to turn the 27-acre Simplex development near MIT into housing, business and retail space over the next 15 years.

Neighborhood groups, who oppose this move in favor of low-cost housing and blue-collar jobs on the Simplex site, are expected to petition the City Council to tighten the area's zoning restrictions.

Lechmere Square in East Cambridge and the area around the Alewife Red Line terminal next to the Arlington line are also undergoing heavy development. Incoming business and neighborhood residents are expected to approach the council with a host of concerns.

The 62-year-old Sullivan, the assistant clerk of the Middlesex Country courts, said he is especially excited that his election as mayor will come on the 50th anniversary, to the day, of when his late father, Michael, was sworn on to the City Council. Every year since has seen a Sullivan serving in city government.

Sullivan's selection as mayor would tip the scales on the School Committee, which now includes three independents and three CCA members.ALFRED E. VELLUCCI