The woman, who managed to wriggle free, also saw him apparently being given oral sex by his secretary, Southwark Crown Court heard.
The woman is one of seven alleged victims of indecent assault by Clifford, 70.
She told the court she worked in an office near Mr Clifford's in 1975. She used to show people to his office when they had meetings, and put calls through to him. One evening, she said, she was walking down the corridor when Mr Clifford came out of his office. She said: "(He) veered towards me, quite quickly, pushed me up against the wall, and sort of pinned me there, with his body. He pushed his tongue into my mouth.
"I made an effort to wriggle and turn and I went under his arm, which was up against the wall, and I walked off."
After that, she felt uncomfortable, the court heard, but she was buying a house and did not want to cause trouble. Not long afterwards, she said she went to his office when the door was slightly ajar. "I saw his secretary, she was on her knees, she appeared to be giving him oral sex while he was in the chair. I was quite shocked, backed away very quickly, " she told the court.
Mr Clifford, of Hersham, Surrey, denies the charges. The trial continues.