It is part of the written testimony Christine Blasey Ford has released before she appears at a crucial Senate panel hearing on September 27.
Judge Brett Kavanaugh, who will also testify, has strenuously denied the accusation.
However, fresh allegations, which Brett Kavanaugh also denies, have appeared as the hearing looms.
His confirmation to the highest US court has been delayed in the wake of the allegations against him.
The nine-member Supreme Court is the final word on US law, including highly contentious social issues and challenges to government policy.
In a written testimony provided ahead of September 27 Senate Judiciary Committee hearing, Christine Blasey Ford says: “It is not my responsibility to determine whether Mr. Kavanaugh deserves to sit on the Supreme Court. My responsibility is to tell the truth.”
Christine Blasey Ford alleges Brett Kavanaugh tried to drunkenly remove her clothing, pinned her to a bed and groped her at a party when she was 15 and he was 17.
“Brett’s assault on me drastically altered my life. For a very long time, I was too afraid and ashamed to tell anyone the details,” she wrote in her prepared statement.
“I tried to convince myself that because Brett did not rape me, I should be able to move on and just pretend that it had never happened.”
Christine Blasey says Brett Kavanaugh and his friend Mark Judge locked her in a bedroom during a small gathering at a house in Washington DC suburbs in the summer of 1982.
“Both Brett and Mark were drunkenly laughing during the attack,” she said.
Mark Judge has disputed the allegations, saying he does not recall the incident.
“I believed [Brett Kavanaugh] was going to rape me,” Christine Blasey said. The fact that he covered her mouth she says “terrified” her the most, and has had “the most lasting impact”.
“It was hard for me to breathe, and I thought that Brett was accidentally going to kill me.”
When Mark Judge jumped on the bed, she says “we toppled over and Brett was no longer on top of me.” She was then able to run from the room.
Brett Kavanaugh is also facing other accusations of assault from three women.
However, he denies Christine Blasey Ford’s allegation “immediately, unequivocally, and categorically”.
The judge also released prepared written testimony ahead of the hearing.
Brett Kavanaugh says: “Over the past few days, other false and uncorroborated accusations have been aired. There has been a frenzy to come up with something – anything, no matter how far-fetched or odious – that will block a vote on my nomination. These are last-minute smears, pure and simple.”
The written testimony suggests Brett Kavanaugh will not try to portray himself as a saint.
He will say: “I was not perfect in those days, just as I am not perfect today. I drank beer with my friends, usually on weekends. Sometimes I had too many.”
He will also say that what he has been accused of is “far more serious than juvenile misbehavior”.
The hearing is scheduled to get under way at 10:00 local time and could last five hours.
There will be opening statements from the leading Republican and Democrat members.
Christine Blasey Ford will deliver her opening statement first.
The 21 senators on the committee will then have five minutes each to pose questions, but while the 10 Democrats are expected to ask questions themselves, it is believed a special counsel will act on behalf of the Republicans.
Christine Blasey Ford will then leave the room and Brett Kavanaugh will enter. She had earlier asked not to be in the same room as the judge.
Brett Kavanaugh will deliver his statement and the same round of questioning will follow.
President Donald Trump has portrayed the events in political terms, accusing the Democrats of trying to block the nomination.
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