The Massachusetts 4th Congressional district includes Newton and Brookline, and stretches west to Wellesley and Fall River. But more than 300 Cambridge residents showed up Saturday night at a fundraiser for Rep. Barney Frank '61 (D-Mass), who is running to capture that seat.

"I think of him as my congressman," said Law Professor Alan M. Dershowitz, who hosted the $15-a-head event at his large home off Brattle St. Noting that several independent organizations have singled out Frank--who first entered Congress in 1980--as the most effective freshman representative. Dershowitz said, "He is one of the most important public officials in Congress. I feel like I have a stake in this seat."

Most of the guests--including a few Harvard professors and several prominent Cambridge politicians--echoed these sentiments, saying that the implications of the race reach beyond the district's boundaries. "If you believe in progressive politics, he is your representative," State Sen. George Bachrach said.

Frank is considered one of the leading young liberals in Congress. He won his first term in what had traditionally been a Democratic district. But the Commonwealth lost a Congressional seat following the 1980 census, and the ensuing redistricting combined Frank's turf with that of 15-year veteran Republican Rep. Margaret Heckler. Three-fourths of the new area is made up of Heckler's old district, and Frank, by all counts, faces a tough fight for reelection.

In the brief remarks Frank made to the crowd before circulating at the Dershowitz gathering, he said he would make the election a referendum on President Reagan's policies. He blames the increasing unemployment in the district on the Administration's budget, which Heckler voted for last May. He said the main part of his strategy is to play economic discomfort against Heckler's polities, explaining that her support for the President "is one of the reasons that Margaret Heckler is vulnerable."

He also contrasted his position with Heckler's on the environment and women's issues. Frank said he heard that his opponent would try to shift the debate in the campaign to funding for abortions and gay rights, both of which he strongly supports. "In that case, I suggest her theme song he "Let's Get Physical,' "he quipped.

Frank noted that the White House and the Moral Majority are targeting him in this election and concluded with his pitch for outside support. "Any election in which you are a candidate can take on importance,' "he joked, adding. however, that this would be a contest of "historic proportions." "I'm going to need your help," he told the group.

The campaign, which has already attracted $300,000, will need $1 million before the November confrontation. Page Gardner, the campaign's financial director, said. They expected roughly $7000 from this event.

Frank said later that half of he money will come from outside the district, adding that he hoped his Harvard background the taught at the Law School and the Kennedy School of Government, and served as assistant senior tutor at Winthrop House would inspire support.

Several professors have contributed or worked with the campaign. Frank said, among them Richard E. Neustadt, Littauer Professor of Public Administration and James Vorenberg, dean of the Law School. Paul A Freund, Loeb University Professor emeritus and Lawrence H. Tribe, professor of Law and former co-tutor with Frank at Winthrop House, both attended the fundraiser.

Local politicians, including city councilor David Sullivan, former school committee member Alice Wolf, and unsuccessful 1980 council candidate Wendy Abt also came to show their support. Others, such as Scott Harshbarger, who is running for Middlesex County district attorney, said he came to express his solidarity with Frank, but also said that the event was "important for me personally as a candidate: many of the people who support Barney are my friends: it gives me an opportunity to talk to them."

James Dolan, campaign manager, said that Frank is now spending three-days a week campaigning and that the effort will move, into full swing by the end of the month. He refused to discuss what current surveys indicate about Frank's chances, but said that Frank is making important inroads into Heckler's traditional base of support, singling out the endorsement from a Fall River labor union that backed Heckler in the last race.