Calling it the "greatest disservice to cities and towns in the history of the Commonwealth," Cambridge City Manager James L. Sullivan told a mock budget hearing last night that the city's government would be unable to provide even police and fire protection within three years if Proposition 2 1/2 passes.

The tax-cutting referendum, Question 2 on Tuesday's ballot, would mean the layoff of one-third of the city's police force in its first year, as well as sharp reductions in levels of other city services, Sullivan told the council, meeting in special session to dramatize what the referendum would mean to local government.

By the time Proposition 2 1/2 is fully implemented, "there will not be sufficient revenue to retain in the service of this city one employee; not a policeman, not a fireman, not a public works laborer," Sullivan said.

Other city officials echoed Sullivan's gloomy forecast. At least three schools would close, and 250 of the city's 850 teachers would lose their jobs, Oliver Brown, a budget analyst for the school department, said.

All branch libraries would shut down, halving the level of service, Joseph Sakey, the city's head librarian, told the council.

And the city's Human Services Department would lose $3 to $4 million in federal matching funds alone since it would be unable to provide many current services, Jill Herrold, who heads the department, said.

Proposition 2 1/2, given a slight edge to win in recent polls, "is the cruelest hoax every played" on Bay State voters, City Councilor David Wylie, who asked for the special session, told his colleagues.

Citing figures showing that property taxes have increased less than the cost of living in recent years, Wylie said supporters of the measure were "greedy-eyed business people with their sharp pencils."

Backers of the referendum have run a series of ads calling the referendum a good way to "send a message" to the state legislature to reform the Commonwealth's tax system.

While Wylie, Sullivan and other opponents conceded that the tax structure of the state's city and towns needs to be reformed to reduce dependence on the property tax, they called Proposition 2 1/2 a risky way of getting across the point.

"It strikes me as unlikely that the state legislature--which has maintained the property tax in its current form for 25 years--will be able to hammer out sensible reform in a single term. And if they don't, it means disaster," Sullivan said.

By gradually reducing local taxes until they reach 2 1/2 per cent of the total assessment of a locality, the proposition would require Cambridge to trim its budget $14 million in the first year, $10 million in the second, and $8, $7 and $6 million in subsequent years.

"The first year, we can cut out libraries and neighborhood clinics; the second year we won't have those things left to cut," Sullivan said.

Taxachusetts

Supporters of the referendum, including Gregory Hiatt, a spokesman for Citizens for Limited Taxation, have accused Sullivan and other local officials of using "scare tactics" in their campaign against the law. "These figures are scary, but they are not tactics--they are exactly how much we would have to cut should Proposition 2 1/2 pass," Sullivan said.

The city's largest taxpayers--Harvard, MIT and Cambridge Light and Electric Co.--would benefit most from passage of the legislation, city experts said yesterday.CrimsonAnthea LetsouDAVID WYLIE