SAN FRANCISCO (AP) _ A secretary suing the world's largest law firm for sexual harassment testified Wednesday her boss grabbed her from behind in a parking lot and said, '''Let's see which breast is bigger.'''

Sobbing occasionally, Rena Weeks recounted the August 1991 incident central to her lawsuit against the firm of Baker & McKenzie and former partner, Martin Greenstein.

Greenstein, 49, who spent 22 years with Baker & McKenzie, was forced to resign in October after the firm investigated Weeks' complaint and allegations from several other former employees. He has acknowledged offensive conduct toward two secretaries, but has denied touching Weeks.

Weeks, 40, contends the firm ignored or concealed other complaints to protect a money-making partner. Her lawsuit seeks unspecified punitive damages. Weeks contradicted the trial testimony of Greenstein and another secretary who was Greenstein's former lover.

Walking ahead of Greenstein, Weeks said, ''I felt Mr. Greenstein pulling me back and putting his arm over my shoulder and dropping something into my breast pocket,'' apparently some M&M candies he had gotten at the restaurant.

His hand touched her breast through the pocket, she said.

Then Greenstein grabbed her from behind by her elbows, put his knee in her lower back, ''pulled me back and said, 'Let's see which breast is bigger,''' she testified.

Greenstein said he merely dropped some candies into her breast pocket after she held the pocket open for him. He denied grabbing her or talking about her breasts.

Weeks testified that the next day she told Greenstein's former secretary Sandra Tischler-Bass about the incident and she allegedly said, '''That sounds like something Marty would do. Let me take care of it. I'll talk to him and I'll tell him to leave you alone.'''

That contradicted testimony Tuesday by Tischler-Bass, who had an affair with Greenstein. Called as a defense witness, she said Weeks never mentioned being grabbed, only mentioning she was embarrassed because Greenstein might have noticed she was not wearing a bral. Weeks has said she was wearing a bra.