Boston — Whatever hopes US Sen. Paul E. Tsongas may have had for a free ride in next November's election have been dashed. Republican Raymond Shamie, the millionaire businessman who last year waged a strong campaign against US Sen. Edward M. Kennedy, has formally declared his candidacy for the Bay State's other Senate seat.
While prospects for a Tsongas toppling in 1984 are seen as less than bright in heavily Democratic Massachusetts, the would-be GOP challenger has proved to be both innovative and anything but easily discouraged.
Mr. Shamie, a conservative and the top Republican vote-getter among contenders for statewide office on the 1982 Bay State ballot, aims to build on that experience in putting together a high-visibility drive to replace the more liberal first-term incumbent.
If successful in winning next year's GOP senatorial nomination, Shamie can be expected to receive plenty of help from within national Republican circles.
The Tsongas Senate seat already has been tentatively targeted by GOP activists from outside the commonwealth as a major political conquest. Although conceding that Shamie goes into the senatorial campaign as an underdog, Massachusetts Republican leaders contend that Tsongas is much less deeply entrenched than is Senator Kennedy, who had held his seat for two decades at the time of his 1982 challenge.
They note that Tsongas, in unseating Republican Sen. Edward W. Brooke six years ago, won by a margin of just more than 200,000 votes among more than 2 million ballots cast.
The 1984 Shamie candidacy, as some GOP leaders view it, could ride on the political coattails of President Reagan if, as now seems likely, the nation's GOP chief executive seeks a second term in the White House. In 1980 Mr. Reagan narrowly carried Massachusetts over Democratic President Jimmy Carter.
In his 1982 senatorial drive, Shamie, then a political newcomer, attracted considerable attention through his hard-hitting campaign, which included a series of full-page newspaper advertisements comparing his positions with those of Senator Kennedy on various issues.
His pursuit of a face-to-face debate with the senator included use of airplanes trailing banners offering a $10,000 reward to anyone who could get Kennedy to debate. Such a program was finally staged about 10 days before the election, in which the senator topped Shamie 61 percent to 39 percent.
This time the Republican senatorial hopeful, who has spent more than $1 million of his own money on the 1982 campaign, has been concentrating on building a statewide grass-roots organization.
Shamie, founder and head of two high-tech firms, formally launched his 1984 campaign with a rally Nov. 28 at a Boston hotel. The event was intended to emphasize the ''diverse ethnic heritage of Massachusetts.'' Shamie, a native of New York, is of French and Lebanese ancestry.
Among names being mentioned as potential Shamie rivals for the Republican nomination include US Secretary of Health and Human Services Margaret M. Heckler and Dr. Mildred Jefferson of Boston. The latter, a black physician and outspoken arbortion foe, sought to compete for the GOP Senate nomination last year but failed to get enough voter signatures to make the party primary ballot.
Senator Tsongas, whose early support for Democratic presidential candidate John Glenn of Ohio displeased some of his party colleagues in the Bay State, also could face a challenge for renomination. So far, however, no intra-party opposition has surfaced.
Shamie suporters suggest that Senator Tsongas is ''more liberal than Senator Kennedy'' and thus could be particularly vulnerable to a strong challenge from a conservative Republican.