A move toward the center could pay off for either Kerry or Shamie

Political moderates may have a tough time finding a US Senate candidate even remotely to their liking on next month's Massachusetts ballot. Democrat John F. Kerry and Republican Raymond Shamie, the two mominees, are about as far apart philosophically as possible, and thus far neither has made much headway in broadening his appeal among thousands of Bay State voters who are neither flaming liberals nor arch-conservatives.

Detracting from the potential Shamie appeal among centrists and liberals within the GOP have been recent disclosures of what he has referred to as ''a brief flirtation'' with the extreme right-wing John Birch Society 10 years ago.

Despite the Walpole industrialist's denunciation of that organization and its positions, his Democratic opponent was anything but willing to let the matter drop - something he may come to regret.

Mr. Kerry in his zeal for political overkill in attempting to portray his opponent as a disciple of the far right, lashed out against the Birch Society. This, as he should have expected, produced an angry response by a spokesman for the group, who questioned Kerry's conduct in the early 1970s as national leader of Vietnam Veterans Against the War. The charge that the Democratic nominee's antiwar activities were ''near-treasonous,'' however unsustainable, could cost him some votes.

The anti-Kerry charge appears to stem substantially from his 1971 appearance before the National Peace Action Coalition, a group then dominated by Trotskyites of the Socialist Workers Party. It is an apparent and regrettable example of guilt by association.

While Mr. Shamie has acknowledged his brief membership in the John Birch Society, the Kerry campaign's attempt to capitalize on it is also to be regretted.

The patriotism or sincerity of neither senatorial candidate should be in doubt. Those who engage in such tactics, for whatever reason, are doing a disservice to the voters. They are clouding what should be the real campaign issue: which candidate would be the most effective senator?

The choice is particularly critical, since neither candidate has had legislative experience. Lieutenant Governor Kerry, to be sure, has held elective office. But his office does not involve much in either the administrative or legislative process, try as hard as he has over the past nearly 22 months to make the most of such opportunities.

If Kerry wins Nov. 6, Massachusetts will be without a lieutenant governor for the next two years. No one on Beacon Hill seems to think this will make much difference.

The Democratic candidate starts with an apparently huge advantage: There are almost four times as many registered Democrats as there are Republicans. But this year Kerry faces no small challenge in getting the lion's share of fellow Democrats to vote for him, plus many independents and at least some Republicans.

Conversely, Shamie certainly seems to be at a big disadvantage. Even if all the nearly 400,000 enrolled Massachusetts Republicans went to the polls and voted for him, he could fall far short of winning. Clearly he will have to attract a lot of the state's 1.1 million independents and nearly 1.5 million Democrats.

The self-made millionaire businessman is counting heavily on many votes from traditionally Democratic blue-collar neighborhoods like South Boston, where some of his positions - such as opposition to forced school busing and public funding of abortion - are more popular than Mr. Kerry's, who supports both.

Shamie failed to attract that voting group, however, when he challenged US Sen. Edward M. Kennedy in 1982. But Ted Kennedy obviously was a more formidable election foe than Kerry.

And then there's the Reagan factor. Some statewide voter-preference samplings indicate the Republican President narrowly ahead in Massachusetts. His coattails look awfully broad right now, and he is actively supporting Shamie.

The Republican candidate clearly will have to convincingly dissociate himself from right-wing extremism; latter-day conservatism among Bay State Democrats has its limits. A slight shift toward the now-vacant center of the Senate campaign might be in order. If nothing else, it could make Shamie less vulnerable to attacks from some critics who view Shamie as farther to the political right than President Reagan.

While not about to count the Kerry votes before they are cast, even in the wake of recent polls showing the lieutenant governor in the lead, supporters of his candidacy clearly expect him to win. Because of this, they apparently see no reason for him to alter his stance to broaden his base and perhaps snare some of the more conservative Democrats.

As the campaign moves into its final days, it would be helpful if both candidates turned away from personal attacks and back to discussion of the issues. Despite facing each other in many debates and forums, Kerry and Shamie have engaged in little in-depth discussion of the serious questions the new senator will have to deal with. And their overly simplistic media advertising has done little more than make their candidacies shopworn.

The lieutenant governor, in his determination to make points and in the process discredit the opposition, may have come on with too much force. He also has tended to talk down to audiences and grab more than his share of debate time.

As expected, Shamie has stuck substantially to a ''no new tax'' position, something which perhaps more than anything else helped him win the Republican nomination by a surprisingly big margin over Elliot L. Richardson.

Whether Mr. Richardson, a GOP moderate, would have been a tougher Republican opponent for Kerry is uncertain. A good many Democratic activists, including some in the Kerry camp, obviously were not disappointed with the Shamie nomination.