The police had managed to keep the two groups of demonstrators apart on Monday and Tuesday. But it was clear just after dawn today that the anti-abortion group was becoming more aggressive after failing to shut clinics through picketing and prayer.

Anti-abortion volunteers arrived at a church headquarters at dawn to be schooled in the basics of crossing police lines and blockading clinics. They were told to carry identification because that would speed their release in the event of arrests.

Operation Rescue's regional director, the Rev. Joseph Slovenec, a minister from the Church of the King in Cleveland Heights, Ohio, said the decision to assault the Amherst clinic was made at about 7:40 A.M. He denied that the action was tied to today's hearing by the United States Supreme Court of an abortion case from Pennsylvania. "The Supreme Court Can do whatever it wants," he said. "The President of the United States can do whatever he wants. We are not here to make a point. . . . We are here to save lives." Tried to Cross Police Lines

At the clinic, the Women's Center, several protesters attempted to dive past a line of Amherst policemen standing in front of the entry way, but they were blocked and wrestled to the ground. Others who tried to move around the police line were chased and restrained.

The police, equipped with plastic handcuffs, subdued the protesters who then sat in the middle of a four-lane highway. Traffic into the area was blocked off, and the protesters were carted one-by-one to waiting police buses and school buses.

As many of those who had been arrested sat in the roadway, anti-abortion protesters on the far side of the highway sang hymns and huddled in small groups. Abortion-rights supporters joined them, and there were several heated shouting matches.

Some Operation Rescue volunteers turned their eyes away from the sight of friends kneeling and sitting handcuffed in the street and bent in prayer. Some watched with a sense of wonder. One 17-year-old girl from Buffalo's Holy Angels Academy High School said she did not think it was her time to take the walk across the street. "I really don't want to get arrested," she said. "I'd have to miss school."