Plan E cleared its initial hurdle yesterday afternoon when Dean Landis of the Law School filed Cambridge City Clerk a petition signed by 9,078 local voters, making mandatory a referendum next November on the proposal for proportional representation and a city-manager form of government.

Although only 5,285 signatures--10 percent of the registered voters at the last state election--were necessary to make the petition valid, the Plan E Committee obtained 9,078 signatures as a show of strength, a member of the Committee explained yesterday.

"The Committee is encouraged," Dean. Landis said upon filling the petition, "by reports from its workers in all parts of the city, who report extraordinary interest in our efforts to make Cambridge the best-governed city in New England."

Lying Low

300 unpaid volunteer workers quietly secured the signatures during the past three weeks. As explained by a member yesterday, the Plan E Committee's strategy is to "lie low" during the spring, conducting an educational campaign and reserving its forces for a whirlwind fight next fall.

By steering clear of personalities, the Committee hopes to avoid the town and gown controversy which developed in the 1938 campaign, when Plan E was rejected by only 1,767 votes out of 46,292 ballots cast.

During the next week, the Cambridge Election Commission will check the authenticity of the signatures on the petition. Then it will come before the City Council, which must certify it to the Secretary of State of Massachusetts.