The Democratic presidential hopefuls brought their road show to Boston tonight, sharing the spotlight with Sen. Edward M. Kennedy (D-Mass.), the man they no longer have to beat.

The lure of six aspirants for the 1984 nomination--all but former Florida governor Reubin Askew--being introduced by Kennedy drew more than 1,500 people at $150 apiece to a state committee dinner that party Chairman Chester G. Atkins said was the most successful ever held.

Kennedy introduced each of the six with a small needle. Of former vice president Walter F. Mondale's recent criticisms of some aspects of the Carter administration record, Kennedy said: "I could have saved myself a lot of trouble in 1980 if I had asked Fritz Mondale to run against Jimmy Carter."

He presented Sen. Gary Hart of Colorado by saying that he is "young, attractive, vigorous and charismatic--but I like him anyway."

Sen. Alan Cranston of California was introduced as a man trying to "keep alive the idea of a 68-year-old president. I may need it someday."

But with all six, Kennedy found much to praise in their records and their associations with the Kennedy family, carefully leaving no clue as to his preference.

The rivals, in turn, framed their standard campaign speeches in ways that gave heavy emphasis to favorite Kennedy themes, particularly the positive role of government in domestic affairs and the need for an all-out effort for nuclear arms control.

The showcase was a stage-setter for the April 9 party convention in Springfield, where the field will compete in a straw vote of about 4,100 delegates for the distinction of being the favorite of Kennedy's constituents. Mondale, the early favorite, is taking the straw vote so seriously that he has assigned one of his top organizers, Paul Tully, a veteran of Kennedy's 1980 campaign, to work full-time in the state.

Hart, who also would like to stake a claim to the Kennedy legacy, is making a major organizational effort for the straw vote, informed Massachusetts Democrats said.

The other speakers on tonight's program--Sens. Cranston, John Glenn of Ohio, Ernest F. Hollings of South Carolina and Dale Bumpers of Arkansas--are rated as long shots in the straw vote.

With the active encouragement of Kennedy and newly elected Gov. Michael S. Dukakis, Atkins is pushing Massachusetts into a more prominent role in the presidential selection process.

In addition to tonight's dinner and next month's straw vote, he is promoting a series of forums on arms control and foreign and domestic policy for later this year, and is trying to give Massachusetts a double dip in the 1984 delegate-selection process.

Atkins has suggested holding an early March caucus in 1984, as close as possible under party rules to the leadoff primary in neighboring New Hampshire. About one-fifth of Massachusetts' 116 delegates would be chosen at the March caucus.

Then he wants Massachusetts to join Ohio, New Jersey and California on the final Tuesday of the primary season--June 5, 1984--with a primary to choose the remaining 90 or so delegates. That way, the state would have an influential voice at both the beginning and the end of the process.

Mondale and Hart have emerged in the early maneuvering as the main bidders for Kennedy's home state.

Hart is seeking to enlist the liberal political activists who gave Dukakis his gubernatorial victory over incumbent Edward J. King, a conservative Democrat, last fall, and he is making a special pitch to college students and other young people.

Mondale, who enjoys a longstanding personal and political friendship with Dukakis, also has support among the more conservative Democrats. Massachusetts House Speaker Tommy McGee, who broke with Kennedy to support the Carter-Mondale ticket in the 1980 primary and who backed King in 1982, was the host of a reception for Mondale this afternoon. Former Massachusetts House speaker David Bartley, a key strategist in the King administration and campaign, said today he is inclined to support Mondale.

Their decisions have caused some Democrats here to discount their earlier estimates that Glenn might do what Sen. Henry M. Jackson (D-Wash.) did in 1976: win the Massachusetts primary with moderate-conservative Democratic support against a field of liberal candidates.

Glenn's chief fund-raiser, Robert Farmer, played the same role in the Dukakis campaign, and reportedly has been putting pressure on the governor to stay neutral, at least until Glenn has a chance to test his popular support in this state.