The rising tide of American conservatism reached even Democratic Massachusetts Tuesday, as Bay State voters voted both for Republican presidential candidate Ronald Reagan and a massive cut in local property taxes.

The presidential vote was something of a fluke; if not for John Anderson's strong Independent showing, Massachusetts probably would have remained safely in the Democratic column.

But the tax-cut vote was no accident. By a 3-2 margin--far larger than anyone had expected--voters approved the controversial Proposition 2 1/2, which will massively reduce property tax revenues which provide most of the financing for local governments in the state.

The size of the vote may very well mean that the state legislature will refuse to make up the lost revenue to cities and towns or to reform the Bay State's tax structure--hopes that prompted even many liberals to support the referendum.

Proposition 2 1/2 has "earned the right to be fully and fairly implemented and tested on its merits," Gov. Edward J. King said Wednesday morning in his first pronouncement on the legislation.

That prospect has municipal leaders terrified. If the referendum goes into effect without state alteration, Cambridge will have to lay off thousands of employees and cancel hundreds of programs, city manager James L. Sullivan insists.

And so, representatives of Cambridge and other municipalities will be on Beacon Hill for the next few months seeking relief and reform. But with legislators terrified of approving any new taxes in the face of Tuesday's overwhelming vote, their task will not be easy.

If they fail to win system-wide reform, they may have one other option. The legislature is thought likely to allow cities and towns to individually override the tax-cut with a two-thirds vote in a special local election.

And that may be enough to help this city--Tuesday, when Cambridge voters went to the polls, exactly 67 per cent of them voted against Proposition 2 1/2.