BOSTON, JUNE 6 -- Massachusetts Democrats, struggling to hold their near-monopoly on political power here, are trying to pin the blame for a disruption at their recent nominating convention on a Republican "dirty trick" run out of the White House.

Rep. Chester G. Atkins, the Democratic State Committee chairman, charged this week that Ron Kaufman, a deputy director of personnel in the Bush administration, was the mastermind behind a last-minute picket line thrown up outside the Springfield Civic Center Saturday that delayed the Democrats' convention by four hours.

Atkins and other top Democrats noted that the picketing was staged by the Springfield police local, a group that noisily endorsed Bush in the 1988 presidential campaign, and that Kaufman, who orchestrated that endorsement, was spotted in Springfield during the weekend.

"I don't think you have to be Dick Tracy to figure out what happened," Max Stern, a prominent Boston attorney hired by the party, said at a news conference announcing plans to sue the police union and Kaufman for allegedly violating the convention delegates' civil rights.

"It's been a long time since the phrase 'dirty tricks' has been associated directly with the White House, but it seems to me that nothing less than that is involved here," added Laurence Tribe, the Harvard Law School constitutional scholar, who is assisting the Democrats in their suit.

Kaufman denied any involvement, saying his role was "none, zero." Although he met with the president of the police local last month in Washington, Kaufman said he was as surprised as anyone when he saw the police picket line on television Saturday morning. "I would never do anything that would in any way, shape or form hurt the president or the White House," he added in a telephone interview.

Robert Jacobson, the union local president, said his members, who are seeking a new contract with the city of Springfield, did not block the hall and broke no laws. "Anybody that says that is a liar," he said.

The controversy arises at what may be a critical time for Massachusetts Democrats, who have won every statewide election since 1974 but who are worried about their hold on the Statehouse.

The concern grows out of the sour mood that has swept over the state since the collapse of the presidential campaign of Gov. Michael S. Dukakis. Since then, the state's budget problems have become worse -- or, according to Republicans, just more obvious -- and many voters are now believed ready to clean house on Beacon Hill.

If so, the Democrats would suffer, because they hold all the top jobs and command four-fifths of the seats in the legislature.

The highest stakes are in the race to succeed Dukakis as governor. At their convention, Democrats endorsed former state attorney general Francis X. Bellotti in an upset over Lt. Gov. Evelyn Murphy. They also gave barely enough votes to John H. Silber, who is on leave as president of Boston University, to qualify him for the three-way Sept. 18 primary.

The blunt-spoken Silber, who has acknowledged that he voted for Ronald Reagan and George Bush, has surged onto the political scene by appealing to Reagan Democrats and depicting himself as a tough "outsider" who can change state government. He topped one pre-convention poll but almost failed to meet the party's 15 percent threshold for making the primary.

In the aftermath of the disrupted convention, questions are also swirling around Atkins, one of the longest-serving state party chairmen in the country. Many Democrats were demanding his head as they stood in the hot sunshine on Saturday waiting for the party to secure an injunction against the picketers.

Atkins said this week that he has no plans to resign, but that he would sit down next January and discuss his role "with the state's next Democratic governor."