The Massachusetts senator urged lawmakers to be realistic, arguing that an 80 percent cut is an aspiration that would be unlikely in the current climate.
On Syria, Kerry was asked about his outreach to Assad, now an international pariah after months of civil war and unending violence against his citizens.
Kerry said there was a moment where Syria reached out to the West but that the moment has long passed.
"History caught up to us. That never happened. And it's now moot, because he (Assad) has made a set of judgments that are inexcusable, that are reprehensible, and I think is not long for remaining as the head of state in Syria," the senator said. "I think the time is ticking."
Sen. John McCain, R-Ariz., a fierce critic of Obama's policy on Syria, said the status quo is unacceptable with the United Nations estimating that 60,000 have been killed and the heavy influx of refugees in Jordan and Turkey.
After a recent visit to the refugee camps, McCain warned that Syrians frustrated with the U.S. response will be a recruitment target for extremists.
"We can do a lot more without putting American boots on the ground," McCain said. "Otherwise, we will be judged harshly by history."
Kerry said it was imperative to continue discussions with Russia and others in dealing with Syria, but he was realistic.
"I don't have optimism," he said.
The hearing was an odd juxtaposition. Kerry has served on the committee during his entire 28 years in the Senate and has chaired the panel for the last four. On Thursday, he sat at the witness table, his voice at times cracking from emotion, facing his colleagues and friends.
Obama chose Kerry to succeed Secretary of State Hillary Rodham Clinton, who introduced the senator. "John is the right choice," Clinton told the panel. "He will bring a record of leadership and service that is exemplary."