POLITICAL LIFE in Cambridge reflects the fierce competition among the diverse nationalities and social strata of the City for attention, power and privilege.

Cambridge has a long history of divisiveness. In 1846, for example, 40 per cent of the citizens in the area opposed the amalgamation and incorporation of the four original villages into one City of Cambridge.

Shortly before the Second World War a controversial Irish mayor was convicted and imprisoned for illegal kickbacks from architects. The outraged citizens searched for a system of local government that would be less corruptable and more representative of the City's Italian, Polish, Portuguese and Spanish immigrants. The state legislature proposed an innovative but unproved scheme of proportional representation: Plan E. The Plan also included a strong City manager and a weak City Council; each was to have a specifically defined purpose.

Proportional representation was heralded in the forties as an effective means of ensuring minority representation with majority control. Any group of voters that numbers more than one-tenth of the population can be sure of electing at least one member of a nine-man council, but a majority group of voters can be sure of electing a majority of the council.

P.R. prevents election landslides by a bare majority. It avoids the need for primary elections, in which voting nearly always tends to be lighter.

Across the Charles, for example, there are no black members of the City Council or the School Committee even though Boston's black population is several times as large as Cambridge's black population. In Cambridge two blacks are on the City Council. One is vice mayor.

The voting system is as complex as the City's ethnic pockets are colorful. Voters must number the names on the ballot in their order of preference instead of making a single "x". An average of 2000 of 30,000 ballots are declared invalid in every election.

Once a candidate reaches one-tenth of the vote, the remainder of his ballots are transferred to the marked second choices and so on. Sometimes there are 30 candidates and a voter has the option of marking his preference all the way of the last name on the ballot. Understanda bly, the counting of votes takes up the better part of a week or longer.

Cambridge's second distinct political feature is the strong City manager-weak City Council scheme. Nine councillors are elected at large by P.R. every two years. The Council elects one of the members as mayor and appoints a City manager. A separate School Committee is composed of six members elected by voters, though.

THE MAYOR chairs the City Council, is chairwoman ex-officio of the School Committee and is the ceremonial head of the City. The Council is the policy making body, deciding only upon three appointments: the City Manager, City Clerk and the City Auditor. The Council meets every Monday night.

The City Manager is the administrative head of the City and legally holds most of the municipal power--except for the School Committee which is independently operated but budgeted through the City manager's office.

Though there are two specific means for taking care of citizens' grievances--the initiative petition and the referendum petition--they have been rarely invoked or enforced by the courts.

In 1972 the School Committee voted 4-3 to oust School Superintendent Frank Frisoli '35 who had served in the system for 33 years. The action touched off a protest that was especially intense in the City's ethnic neighborhoods.

Almost 17,000 residents signed petitions asking for a public referendum on Frisoli's firing. Although nearly 50 per cent of the voters who put the School Board in office were against the firing, the board voted to deny the referendum. Citizens for Frisoli filed suit against the mayor, but a country judge ruled that the ultimate power lay with the School Board and dismissed the case.

The amended City Charter makes it clear that the City manager and his staff is to handle municipal affairs and authorize civil servants to do specific jobs. The City councillors, by law, are forbidden to tamper with this process at the risk of a $500 fine or a six month prison sentence. Violators also are forbidden to serve the City in any future capacity, elective or otherwise.