Sen. Edward M. Kennedy, the Bay State's best known Democrat, can be expected to declare within the next few weeks, probably shortly after the new year, that he again will seek the presidency.
This is the expectation within Massachusetts Democratic circles, although nobody appears to have the official word from the senator, who has not discouraged speculation concerning his political plans.
For now, Mr. Kennedy has set up a ''national presidential exploratory committee,'' the Boston Herald American reported Tuesday. Such a committee would test the political climate for a candidacy and begin fund-raising efforts if the senator decides to run, a Kennedy spokesman said.
Kennedy's Bay State boosters anticipate that former Vice-President Walter F. Mondale, who spent a day here in late October to campaign for the senator's reelection bid, also will be in the race - and making a strong run in the Massachusetts presidential primary in March 1984.
Although the most recent senatorial primaries show Kennedy's support among Massachusetts Democrats is consistent (71.40 percent in 1976 and 71.82 percent in 1982), his White House prospects may have been dimmed by his poorer-than-usual showing in the Nov. 2 general election.
Official returns from the state's 351 cities and towns gave him 1,247,084 votes (or 59.3 percent), but this figure was significantly less than the 66.5 percent he garnered six years ago.
And his latest showing pales in comparison with his performance in March 1980 (64 percent of the vote), when he defeated former President Jimmy Carter in the Massachusetts Democratic presidential primary.
Since Kennedy won his first election two decades ago, only once has his portion of the total vote been smaller. That low was 58.85 percent in November 1970, his first campaign after the accident on Chappaquiddick Island in which a woman passenger in his car was killed.
Kennedy aides are unwilling to concede that the senator's failure to do as well this time could indicate a decline in his popularity at home, noting he won nearly six of every 10 votes cast. His reelection, they say, came in the face of a concerted drive by conservative political forces to embarrass, if not unseat, one of the nation's most prominent liberal senators.
Contributing to the senator's weaker showing in the latest balloting was Raymond Shamie, his millionaire Republican challenger, who invested considerable funds of his own to conduct a year-long, hard-hitting attack on Kennedy's voting record.
The GOP political newcomer polled 784,602 votes, 37.29 percent of the 2,103, 780 cast. The latter total includes 19,083 votes cast for other senatorial candidates and 53,011 blank ballots cast. How Kennedy has fared in his home state US Senate elections In Massachusetts 1962.....54% 1964.....74% 1970.....59% 1976.....67% 1982.....59%