Chelsea Clinton joined her mother and a bevy of elected officials and Jewish leaders at the news conference at New York's City Hall.
The first daughter gave no speech but said she would participate "on and off" in her mother's campaign for U.S. Senate.
Chelsea Clinton rode along briefly with her mother's listening tour last year, but hadn't been seen on the campaign trail since. She smiled shyly, shook hands with reporters and playfully fanned one of her mother's aides. She greeted a little girl before kissing her mother goodbye.
"She's going to be coming and going as she chooses," Hillary Clinton said of her daughter on Monday. "I believe in permitting her to make those decisions. You'll be seeing her sometimes, which will be a delight for me, and that's all I can tell you."
The news conference was to announce Mrs. Clinton's support for a worldwide petition drive to free the Iranian Jews, who may face the death penalty if they are convicted of spying. Clinton's GOP Senate opponent, Rep. Rick Lazio, is helping to collect signatures in Congress.
Democrat Clinton still had her daughter on her mind when she spoke later Monday at the commencement for Forest Hills High School in Queens, which was held in the Nassau Coliseum on Long Island.
She told the 600 graduates and their families, "When Chelsea graduated from high school, I certainly remember sitting there in the audience as so many parents and proud relatives are today. It was just as much a rite of passage for Bill and me as it is for all of you, because you as parents are entering a new stage of life as well with this important step by these young men and women."
Clinton reiterated campaign proposals for making college tuition tax deductible and providing college scholarships to students who agree to teach in underserved public schools.
Also Monday, Lazio attacked both the president and the first lady for not doing more to fight rising high gas prices.
Using a suburban Buffalo service station as a backdrop, Lazio said Mrs. Clinton should "get out of the motorcade, check the prices at the pump and join me today in fighting for the repeal of the Clinton-Gore gas tax to help get these gas prices down for New Yorkers."
The Long Island congressman called for the permanent repeal of a 4.3-cents-per-gallon gas tax increase introduced in 1993 by the president. He also said the federal 18.3-cent gas tax should be suspended for six months, OPEC nations should be pressured to increase production, and the nation's strategic petroleum reserve should be opened immediately.
"New Yorkers are being gouged at the pump," said Lazio.
The president sought to temper calls for rolling back the federal gas tax, saying Monday that such a move would disrupt federal highway projects and rovide little relief to American motorists.
Speaking to reporters in Washington, Mr. Clinton urged continued pressure on the oil industry to keep prices falling and suggested that Congress think hard about the far-reaching ramifications before cutting the gas tax.
His wife's campaign countered Lazio by saying that the congressman missed a recent vote that could have helped lower fuel oil prices in New York. On June 15, the House voted 195-193 to reject an amendment that would have created a 2 million-barrel home heating oil reserve for the Northeast.
"If Congressman Lazio really cared about this issue, why did he miss the vote to establish the Northeast Oil Reserve?" Clinton campaign spokesman Howard Wolfson said in a statement.
Clinton herself went after Lazio on Monday.
"Months and months ago, I advocated a Northeastern oil reserve that I thought would be helpful in helping to lower the cost of home heating oil here in New York," she said. "We could have passed that. He missed that vote."
Lazio missed the House vote, so he could catch a flight back to New York to keep to his campaign schedule the next day.
Finally, Clinton campaign spokesman Wolfson confirmed a report in the New York Post that the first lady would attend a fund-raising luncheon for her campaign Friday at the Park Avenue home of retired insurance executive Walter Kaye.
Kaye, a friend of Monica Lewinsky's mother, recommended Lewinsky for the White House internship that led to her sexual relationship with the president.