"When we send our young men and women into harm's way, we have a solemn obligation not to fudge the numbers or shade the truth about why they're going," said Obama, who is heavily favored to become just the third black elected to the Senate since Reconstruction.
Obama described Democratic presidential candidate John Kerry as a war hero who has long made "tough choices when easier ones were available." He faulted the war policies of the current commander in chief without mentioning him by name.
The 42-year-old Obama, a rising star in the Democratic Party, followed a succession of party veterans to the stage of the FleetCenter Tuesday, including Senate Minority Leader Tom Daschle, Rep. Dick Gephardt and former Vermont Gov. Howard Dean.
In a featured speech, for embarking on a "misguided war" in Iraq, and said Kerry offered the "hope of real victory against terrorism and true security at home."
Kennedy, the patriarch of the country's most enduring political dynasty, called his fellow Massachusetts senator "the right leader for this time in history."
The oratory on the second night of the convention meshed with Kerry's own campaign rhetoric. In an appearance in Norfolk, Va., the Massachusetts senator issued a fresh challenge to Mr. Bush to implement many of the anti-terror recommendations made by the Sept. 11 commission.
"Backpedaling and going slow is something that America can't afford," said Kerry, who is making a waterborne arrival in the convention city on Wednesday.
Sen. John Edwards of North Carolina, Kerry's vice presidential running mate, flew to Boston in advance of his own convention speech Wednesday.
Kerry's wife, Teresa Heinz Kerry, and Ron Reagan, son of a conservative icon, also had prime speaking slots Tuesday night.
Democrats met while President Bush was at his Texas ranch. White House spokeswoman Claire Buchan said he hadn't watched any of the opening night of the convention, and she didn't expected him to tune in for the second night, either.
Not so his campaign surrogates. They issued a ceaseless stream of criticism of Kerry and his convention proceedings, designed to depict his as a flip-flopping liberal weak on foreign policy. "With Sen. Kerry, we have seven different positions on his vote against the $87 billion for Iraq (and Afghanistan)," argued Sen. Norm Coleman, R-Minn.
In his speech, Obama offered his own life as an example of uniquely American possibilities. The son of a white woman from Kansas and a black man from Kenya, he said people don't expect government to solve all their problems but do want help for "a decent shot at life."
"They sense, deep in their bones, that with just a change in priorities we can make sure that every child in America has a decent shot at life and that the doors of opportunity remain open to all,'' he said.
He said Kerry would tackle the nation's economic problems, expand health care opportunities, work for energy independence and preserve civil liberties in a time of terrorism.
Obama added: "Just as Lt. Kerry did not hesitate to risk his life to protect the men who served with him in Vietnam, President Kerry will not hesitate one moment to use our military might to keep America safe and secure."
With Mr. Bush's campaign constantly assailing Kerry as a liberal trying to run from his record, Obama said "there are those who are preparing to divide us" in the campaign ahead.
Referring to so-called red states that traditionally vote for Republicans and so-called blue states that traditionally support Democrats, he said, "We worship an awesome God in the blue states and we don't like federal agents poking around our libraries in the red states. We coach Little League in the blue states and have gay friends in the red states."