The calendar says it's only April, but two local State House incumbents are already locked in a deadly game of musical chairs.

This year's state redistricting plan reflects drops in the Cambridge and Somerville populations by merging the districts of Reps. Peter A. Vellucci (D-Cambridge) and Marie E. Howe (D-Somerville).

The 29th District of Middlesex County, which they are competing to represent, is now divided almost evenly between the cities, with 9000 voters in Cambridge and 8000 in Somerville.

As a result, these two veteran politicians will square off in what could be the most expensive state representative campaign in Massachusetts history. While the two Democrats ran almost unopposed in 1986, they are certain to wage heated campaigns throughout the spring and summer months, culminating in the September 15 Democratic primary.

Although the candidates promised positive campaigns using differences on issues, both Howe and Vellucci have already attacked each other over endorsements, finances, volunteer strength and voting and attendance records. Both campaigns have also hinted at charges of personal indiscretions.

Peter Vellucci, son of Cambridge Mayor Alfred E. Vellucci, is in his third term in the State House. To defeat token Republican opposition two years ago, the Cambridge representative spent $4000. But this time Vellucci says he will be in serious trouble unless he receives contributions totaling $75,000 to $100,000.

"If we get anything less than $60,000, the situation will really be grim," said Clifford Truesdell '66, Vellucci's campaign manager. He said Vellucci has already received more than $24,000 in contributions.

Howe has been in the State House for more than 23 years. The Somerville representative declined to say how much she had raised, but a campaign finance report shows she had received more than $21,000 by the end of 1987. Her contributors include many trade unions and Senator President William M. Bulger (D-Boston).

She called Vellucci's claim to have raised nearly $30,000 "nothing but a lie" and also said the Cambridge representative exaggerated his claim to have sent 180 volunteer canvassers to the polls on Super Tuesday.

Vellucci describes himself as a neighborhood politician who cares about the working people of his district. "This is going to be a neighborhood-oriented grass-roots campaign," Vellucci said.

Along with the support of his working-class constituents, Vellucci has actively sought backing from political colleagues in Boston and Washington. He said he has received endorsements from U.S. Reps. Edward Markey and Barney Frank, both liberal Democrats from Eastern Massachusetts.

The name of Sen. Edward M. Kennedy '54 also appears on invitations to a Thursday night fundraising dinner for Vellucci.

Howe charged this week that the name appeared there without Kennedy's permission, but Mark O'Connor, a spokesman for the senator, said that although Kennedy planned to remain neutral during the primary, his staff had given Vellucci permission to put his name on the invitation.

Howe derided Vellucci's efforts to receive endorsements. "The only way he can get a vote is through hype. He is not in touch with the people. That's why he has to have the heavyweights," she said.

Meanwhile, Vellucci has focused on differences over issues and on publicizing "flip-flops" among Howe's votes on Beacon Hill.

Specifically, Vellucci said Howe changes her stand on abortion to suit the audiences she is addressing. Citing Howe's June 3, 1987 vote for a bill restricting abortions for minors, he said Howe's views on the question remain pro-life and said they have been so for 20 years.

"Howe really worries me because she keeps changing her views. She claims to be pro-choice but recently appeared in front of a group and said she was pro-life," Vellucci said. "When it comes to women's issues, there's a big difference between her and I," he added.

Mass Choice, a pro-abortion lobbying group, has endorsed Vellucci, said Melissa Kogut, a spokesman for the organization. "Vellucci has a strong and consistent pro-choice voting record, said Kogut. "With Howe, we were confused because only in the last two votes has she voted with us," she added.

Howe said she had a right to modify her views to reflect the interests of her constituents. While she said that for most of her 23 years on Beacon Hill she had voted against abortion, she now votes pro-choice because her constituents favor free access to abortion.

"You have to believe in a woman's right to elect and choose. [She] should also have the right to carry the pregnancy to full term. While I do not oppose the law, I have my own personal convictions," Howe said.

In a rare move for a legislative campaign, Vellucci has hired political strategist Michael Goldman. The consultant has broad experience in statewide and Congressional races, including the 1986 campaign of Rep. Joseph P. Kennedy II. Goldman said the Vellucci side will stress issues and not the personalties of the candidates in the campaign.

"The way you win is to compare and contrast Howe and Vellucci on the issues. It's fair to say that Vellucci's a more liberal voter," Goldman said. He said Vellucci supports comparable worth pay for women, gay rights and strict gun control while Howe has not always done so.

Truesdell echoed Goldman's stress on issues. "There are clear political differences between the two. Marie, for instance, supports funding for parochial schools and only got religion on [House rules] reform four years ago. Peter was elected as a House rules reformer," Truesdell said.

Howe said the attempt to portray Vellucci as a more "progressive" candidate would not work. "I have substantive issues to stand on," she said. She also criticized Vellucci's State House attendance record.

The Somerville representative said that years before Vellucci's freshman term, she had supported gay rights and the activities of Amnesty International, as well as human rights efforts in Northern Ireland. In addition, Howe said she has worked closely with unions and that she has had her picture taken with Elanor Smeal, former president of the National Organization for Women (NOW).

Vellucci said his ratings with liberal groups were considerably higher than Howe's. He said he had voted with NOW's recommendations on 10 of 11 key votes in 1985-86, while Howe matched the group's views on half of them.

"Marie should win the award for taking pictures and going to funerals," Vellucci said. "I should win on issues."

Almost the only thing the candidates can agree upon is the closeness of the race. Vellucci is clearly the favorite in Cambridge, but Howe has strong support in Somerville.

"This is a very difficult race," said Goldman. "Marie has been in a lot of wars and has a strong base in Somerville. We're going to have to educate [voters] on who is the progressive candidate."

Although Somerville Mayor Eugene Brune has endorsed Vellucci, Howe has many backers among the city's leadership. Mary Tomeo, a former city tax assessor, said Howe has worked hard for the elderly and for the Portuguese immigrant community in Somerville.

"Marie is a down-to-earth, determined person who's done a lot for Somerville. If you asked her to do something, she would always reply," Tomeo said.

Howe also was praised by Somerville Alderman Michael Capuano, who described her as an unusual politician, one not afraid to take on the establishment. "If you don't know Marie Howe, you haven't been living in Somerville," he added.

Capuano said both Vellucci and Howe had distinguished records in the House but that the race will be determined by personalities, not issues.

"Seventy percent of people vote on a personal basis. It seldom comes down to issues. This is going to be a good campaign for politicians to watch and learn from," said Capuano.