Speaking in the broad thematic strokes that more voters expect from Mr. Obama, Mrs. Clinton invoked Robert F. Kennedy by name as she said she was running to strengthen the United States for “the next generation” of Americans. She bluntly added that there was “no guarantee that we will remain a great country” unless all people contribute to the nation’s needs.

“One of the main reasons I decided to run for president is because I will not stand by and see our country break faith — that we would leave American worse off than when we found it,” Mrs. Clinton said at California State University-Los Angeles.

“There is no guarantee we will remain a great country,” she continued. “It’s up to each of us in our own way, in our own time, to make the contributions, to set the goals and achieve them.”

Referring to Mr. Obama, Mrs. Clinton said at one point, “My opponent will not commit to universal health care,” triggering a round of boos. “I do not believe we should nominate any Democrat who will not stand here today, tomorrow, or any day” who will not explicitly support universal health insurance,” she added.

Mr. Obama has said his health care plan would sufficiently lower costs to make insurance affordable for Americans to obtain it. But unlike Mrs. Clinton, he would not require all people to purchase or obtain it — a key difference, she argues.

Mrs. Clinton also touted her experience in public life, and by extension contrasted it with Mr. Obama’s record as a state legislator and three years in the United States Senate.

“There will be no guesswork — I’m not asking you to take a leap of faith — I’m asking you to hire me to do the hardest job in the entire world,” Mrs. Clinton said, sparking chants of “Hillary! Hillary!” from the crowd.

Mrs. Clinton also criticized Mr. McCain by name, citing his remark about American soldiers in Iraq.

“He’d be perfectly happy to be there for 100 years,” she said. “I just want you to think about this — I believe we can have an election this time where all of the issues, including national security, are ones where democrats can stand and proudly promote.”

Mrs. Clinton referred to Mr. Kennedy’s visit to East Los Angeles decades ago — and also praised the labor leader Cesar Chavez — with a clear purpose in mind. Not only is she battling Mr. Obama’s endorsements from Senator Edward M. Kennedy; Robert Kennedy’s widow, Ethel; and President Kennedy’s daughter Caroline, but she is also seeking a mandate of support in Tuesday’s nominating contest in California and 21 other states from working class voters, Hispanics, union members, and young people.

She also said she wanted to “tackle poverty” — the chief cause of her former Democratic opponent, John Edwards, whose endorsement both she and Mr. Obama are seeking.

“We need a doer, we need a fighter, and we need a champion who once again gets up every day in the White House,” she said.

“What we have to do together is to seize this moment and give each and every one of us a role to play in the new America I see,” she said.

“The America I see, we will once again commit ourselves to making every single child have the same chances no matter where he or she is born, to live up to their God-given potential,” she continued.

“In the America I see,” she added, all people will have universal health care and universal pre-kindergarten, access to an affordable college education, and protection from “abusive lending practices.”

Mrs. Clinton left Los Angeles in the early afternoon to hold rallies on Saturday in two other states with nominating contests on Tuesday, Arizona and New Mexico, before heading on to Missouri, where she was scheduled to land at 2 a.m. Sunday.