President Barack Obama said on Friday he expected a tough vote this weekend, but Democrats were poised to make history when the House of Representatives votes on his healthcare overhaul bill.

"Right now we are at the point where we are going to do something historic this weekend," Obama told a raucous audience at George Mason University, as Democratic congressional leaders scrambled to round up support for the plan to revamp the $2.5 trillion medical industry.

"If this vote fails, the insurance industry will continue to run amok. They will continue to deny people coverage. They will continue to deny people care. They will continue to jack up premiums 40 percent or 50 percent or 60 percent as they have in the last few weeks," he told the rally.

"That's why they're pouring millions of dollars into negative ads. That's why they're doing everything they can to kill this bill," Obama said in a fiery speech.

"The time for reform is now," he said.

After more than a year of intense debate, the House is expected to vote on Sunday on the sweeping healthcare overhaul, intended to extend insurance coverage to 32 million uninsured Americans.

The bill has faced solid Republican opposition, and Obama and his fellow Democrats were struggling to ensure enough votes from Democrats, who hold a majority of seats in both houses of Congress, to ensure its passage.