June 5, 1981

Craig S. Crimmins was found guilty yesterday of murdering a violinist at the Metropolitan Opera House last July 23. The 22-year-old former stagehand remained impassive when the verdict was announced, but his girlfriend, Mary Ann Fennell, wept loudly. After Mr. Crimmins had been led away, she kept repeating, while sobbing and saying: ''They're wrong, they're wrong. He didn't do it.'' The jury of seven women and five men in State Supreme Court in Manhattan determined that Mr. Crimmins had killed Helen Hagnes, who had been performing in an orchestra for the Berlin Ballet, by pushing her down an airshaft in his flight following his attempt to rape her. Maximum Term 25 Years to Life

As investigators searched today through material taken from his home and car, a man held for questioning about the slayings of 28 young blacks denied any involvement in the crimes and accused the authorities and the press of slandering him. Wayne B. Williams, a 23-year-old black, was held through the night and predawn hours by the Federal and local authorities before being released without being charged. But a four-hour search of his belongings produced blankets, clothing, carpet samples and other articles that were being analyzed by crime laboratory investigators for fibers, animal hairs or any other trace evidence that might link them to any of the deaths, which have been recorded in the last 22 months. Mr. Williams, an electronics expert and broker of local musical talent, told reporters after he was released early today that agents of the Federal Bureau of Investigation had repeatedly accused him of the murders and had warned him, ''It's just a matter of time before we get you.'' 'I'm a Prime Suspect' ''I still think I'm a prime suspect,'' Mr. Williams said, and at another point said the press had ''ruined my reputation.'' An F.B.I. spokesman, William McGrath, said, ''We have no comment about any of his allegations.'' The developments of the past 24 hours, which follow almost two years of disappointments and frustrations, have the city dizzy with anticipation.

Despite earlier pledges to keep its tax legislation lean and simple, the Reagan Administration has engaged in a flurry of adding ''sweeteners'' to capture crucial votes. And now the Democrats, who will draft their legislation later, may try to match or improve on the most attractive parts of the President's new package. The prime targets of the legislative maneuvering by the Administration and the House Democratic leadership are the votes of conservative Southern Democrats and wavering Republicans who hold the key to victory. With his announcement today, the President drew the battle lines against the Democratic leaders in the House and set the stage for another showdown, probably late this month.

In preparing for the visit of Secretary of State Alexander M. Haig Jr. to China next week, the Reagan Administration is moving toward decisions that will give more of a military cast to Chinese-American relations. Specifically, according to American officials, there is strong pressure to remove China from the list of Communist countries subject to special export controls. This would allow for the transfer of military technology such as the engine and electrical equipment from the new F-16 fighter plane and for the sale of TOW antitank missiles. Common Anti-Soviet Front Sought A number of officials see this as a way of strengthening a common anti-Soviet front, but some also see the prospective offer as an effort to induce Peking to accept the sale of an advanced type of fighter plane to Taiwan.

The State Court of Appeals ruled today that New York City did not have to pay police lieutenants and sergeants who were given supervisory positions more money simply because of their new designations. The 4-to-3 decision by the court, the state's highest, will save the city about $30 million in back salary and pension pay, according to Alfred Weinstein, assistant corporation counsel. Mr. Weinstein said that the city was ''pleased by the decision'' and that it might serve as a precedent for an associated case involving 1,000 patrolmen detailed to work in the detective division who have brought suit for financial compensation for their work. Their suit could cost the city $26 million in back salaries and pensions.