Kerry Kennedy’s drugged-driving trial kicked off Monday with her lawyer touting her famous lineage — and her matriarch mom Ethel making a rare public appearance in court to support her.

“She is a daughter of Ethel and Robert Kennedy and a niece of our past president, John Fitzgerald Kennedy,” said high-powered Kennedy lawyer Gerald Lefcourt to jurors in the packed White Plains court room, where two of Kerry’s brothers, Robert F. Kennedy Jr. and Douglas, also sat.

Lefcourt rattled off other personal tidbits about his “serious and religious’’ client — even the fact that she has two daughters in Ivy League schools — but acting State Supreme Court Justice Robert Neary was clearly unimpressed.

“Mr. Lefcourt, this isn’t evidence,’’ the judge sniffed.

Kerry Kennedy, the ex-wife of Gov. Cuomo, is expected to take the stand in her own defense as early as Tuesday afternoon.

She was arrested the morning of July 13, 2012, after her 2008 silver Lexus SUV hit a tractor trailer on I-684 in Westchester. Kennedy, 54, didn’t stop and instead drove with a blown tire for another 5 miles before finally pulling off on a highway exit, where she struck a guardrail as she tried to drive away again.

Lefcourt claimed Monday that his client was “sleep driving’’ after accidentally taking an Ambien instead of her thyroid medication.

“This case is about a mistake, plain and simple,” he said.

But prosecutors said Kennedy had to know she was under the influence of the sleeping aid when she first crashed because the drug kicks in quickly.

“She would have realized her mistake and she would have known” she had taken the wrong medication, prosecutor Stefanie DeNise insisted.

“She is responsible for her actions that day … by failing to stop her car and pull over.”

Kennedy’s mom, the 85-year-old widow of Sen. Robert F. Kennedy, listened intently after entering the courtroom in a wheelchair. Dressed in a gray-and-white checked jacket, dark gray pants and sneakers, she was accompanied by family friend Joe Armstrong, former publisher of Texas Monthly, and an unidentified woman.

Bobby Kennedy exclusively told The Post that his sister should be found not guilty of driving under the influence because she’s a human-rights activist whose life-saving work would be severely curbed if she was sidelined by jail.

Kerry faces a single count of driving while impaired by drugs. If convicted, she could lose her license and land up to a year behind bars.

Lefcourt insisted to jurors that his client “is not seeking any advantage here because of her famous family.

“On the other hand, she should not be punished because of that family,” he said.

Kennedy told cops the day of the accident that she may have mistakenly taken the drug Zolpidem, sold as Ambien.

Four days later, she told reporters that her doctors believed that she suffered a “complex partial seizure’’ at the time, caused by a previous head injury.

But after drug tests revealed Ambien in her system, her legal team switched back to her original defense.

Lefcourt on Monday said Kennedy had rented out her home for the summer and was staying in an apartment over the garage while preparing for a trip to Africa. She put the Ambien, which she uses for overseas travel to sleep, next to her thyroid meds on the counter, he said, causing the mix-up.

He said she was fine leaving the house and navigating tight turns on her way to I-684.

But once she hit the highway, “she forgets what happened next. The Zolpidem kicks in, and she shuts down,’’ he said.

He said she only started sobering up after being taken to at Northern Westchester Hospital. Kennedy consented to blood and urine tests because she wanted to know what happened to her, he said.

“All this shows that she certainly didn’t know anytime while driving” that she was under influence of Ambien, the lawyer said.

Lefcourt said Kennedy’s Ambien “was a valid prescription, this was not a party drug.”

Witnesses described the accident for jurors, including Henry Myers, who called cops after seeing her hit the truck.

Under questioning from assistant DA Doreen Lloyd, he said he was at stop light getting ready to get on 684 south behind a silver Lexus with “Joe Kennedy for Congress” and “Riverkeeper” bumper stickers.

Kennedy’s driving was erratic from the moment the light turned green, he said.

“She swerved onto the grass, I thought maybe she was on her phone or something” but then swerved again as they got onto highway,’’ he said.

“The car took off pretty quick, got into the middle lane [and] then was swerving into the other lanes” at 70 to 75 mph without signalling, Myers said.

“A tractor trailer came up beside her, the Lexus hit the side of him, I saw smoke. I figured the car would stop but then as we kept going I saw a big piece of tire roll down the shoulder,” he said.

Kennedy got off at Exit 3, and Myers called 911.

A second witness, William Carlino of Armonk, whose kids go to school with Kennedy, came upon her in her car at an intersection off Exit 3 and saw her slumped against the steering wheel.

He said he didn’t recognize her at the time.

“I asked if she was OK, and she nodded in the affirmative,” he said, adding that she appeared “a bit disoriented.”

She then got back in the car and started to back up, Carlino said.He said he told her to stop, but she kept going, hitting the guard rail. That’s when he called cops, he said.

Under cross examination, Lefcourt asked, “She was out of it?”

“Yes, I would say, yes,” Carlino answered.

North Castle Police Officer Joel Thomas, under questioning by DeNise, said that as he questioned Kennedy, “Her speech was slow and deliberate.

“I asked her if she was diabetic or on any medications that would cause this condition. She said she was not.”

“She was asked to recite the alphabet from the letter J to the letter T. She performed it successfully without mistakes,’’ he said.

He said he then asked her to stand on one leg.

“She did not perform the test successfully,’’ the cop said. “She was unable to maintain her balance.”

Based on that and other balance tests, “we thought she was impaired,’’ he said.

Video from a police car shows her at one point in the back of the cruiser looking out the window with her arms crossed. She’s dressed in shorts, a tank top and sneakers; she has said she was headed to the gym at the time of the accident.

After a few minutes, it appears that her head slumps forward in the car and she’s sleeping.

After another roughly 11 minutes of the film were shown in court in which Kennedy does nothing but sleep, the frustrated judge asked, “How much longer do we see this?”

Kennedy arrived to court dressed in a conservative gray coat, tights and knee-length dress with small pumps. She was accompanied by her lawyers and smiled as reporters shouted questions.

Kennedy got permission from Judge Neary to miss jury selection last week because she was on a trip to Western Sahara promoting human rights.

She had hoped to avoid a trial, but her bid to have the case tossed failed last week after Neary denied her motion to have the case dropped because she supposedly took the sleeping pill by accident.

Even if Kennedy accidentally drugged herself with a sleeping pill, she broke the law if she kept driving after feeling the effects, prosecutors argue.

During jury selection, Neary did not allow defense lawyers to ask potential jurors about their political affiliations but said they can ask if they have any “strong feelings” about the Kennedy family.

In addition to character witnesses, the defense plans to call a Massachusetts pharmacologist, Dr. David Benjamin.

The prosecution’s witness list includes Elizabeth Stratton as an expert on Zolpidem.