By Yasmeen Abutaleb and Richard Cowan

WASHINGTON (Reuters) - Thirty-two million Americans would lose their health insurance by 2026 if Obamacare is repealed without a replacement, the U.S. Congressional Budget Office reported late on Wednesday as President Donald Trump pushed fellow Senate Republicans to reach an agreement on overhauling the country's healthcare law.

Senate Majority Leader Mitch McConnell planned to hold a vote for a straight repeal of the Affordable Care Act next week after a bill to repeal and replace collapsed on Monday with the Republican party sharply divided.

According to the CBO, a nonpartisan office that analyses pending legislation, 17 million Americans would lose health insurance alone in 2018 with a repeal while premiums on individual insurance plans would rise 25 percent next year and double by 2026.

Trump told 49 Republican senators at a White House lunch on Wednesday that he wanted more than a straight repeal.

After taking a hands-off approach to the healthcare debate last week and suggesting on Tuesday that he was fine with letting Obamacare fail, Trump on Wednesday demanded that senators stay in Washington through their planned August recess until they can find common ground on healthcare.

"We're close. We're very close," Trump said at the start of the meeting.

He demanded that lawmakers keep their campaign promises to repeal and replace Obamacare and find a new approach to healthcare.

"We can repeal, but we should repeal and replace, and we shouldn’t leave town until this is complete," he said.

After the lunch, McConnell said he will go ahead with a vote early next week to begin debate on a repeal of the ACA, former President Barack Obama's signature legislation, despite indications it will fail after the defections on Tuesday of at least three Republican senators.

Moderate Republican Senators Susan Collins, Lisa Murkowski and Shelley Moore Capito said they oppose McConnell's plan for a repeal that would take effect in two years, giving Congress time to develop a replacement. All three attended the lunch.

With Democrats united in opposition to repeal, McConnell can only lose two votes from Republicans' 52-48 majority in the 100-seat Senate to pass healthcare legislation.

(Writing by John Whitesides and Lisa Lambert; Additional reporting by Susan Cornwell, Richard Cowan, Yasmeen Abutaleb and Susan Heavey; Editing by Mary Milliken and Leslie Adler)