''I went into many offices in which no one was in,'' he said. Then he got to Mr. Packwood's office and, using a skeleton key, unlocked the door.

''Maybe he thought there was an intruder, and he tried to push the door closed,'' Mr. Giugni said.

Senator Packwood thought no such thing. He had placed a heavy chair in front of one door to keep the police from forcing it open. That worked. He bolted another door. That did not work. The key unbolted it. ''It was their mass against my mass,'' Senator Packwood said.

Senator Packwood's mass was placed in the Senate's history book alongside that of Senator Kenneth McKellar, who was the last member of the Senate to be arrested and compelled to attend a quorum call. Found at a Hotel

The Tennessee Democrat was one of seven Southern senators hiding in November 1942 in an attempt to block action on a bill repealing the poll tax. He was taken into custody in a hotel. Senator Packwood said he bore no animosity toward Mr. Giugni (pronounced JOON-ee), saying, ''If ever there was a gentleman, who didn't want to do his duty, it was Henry.'' ''I have a job to do,'' said Mr. Giugni. Senator Packwood called a news conference in a Capitol gallery and invited the sergeant-at-arms to join him, which he did. Mr. Packwood used the incident to win attention for his complaints about the bill, which would institute voluntary spending limits in general election campaigns for the Senate. Arm Was Bandaged

He frequently raised his bandaged arm to eye level to emphasize a point, and each time that he did so there was a chorus of camera shutters clicking. He warned that the Democratic leadership had offended the bipartisan comity needed to win passage of legislation and said the incident would make Republicans more partisan.

On close issues, he said, Republican leaders will tell wavering members: ''Remember Packwood. Remember what they did.''

A few hours after the Packwood press conference, the Democratic majority leader, Senator Robert C. Byrd of West Virginia, called one of his own. ''Senators are supposed to be grown-up people, not kids,'' he said. ''The Senate shouldn't have to arrest senators. They should come to the floor. Those who played games and boycotted the meeting now want to feel put upon.''