WASHINGTON/NEW YORK - White House hopeful Elizabeth Warren on Friday outlined how she would implement Medicare for All during her first term, including new legislation in her first 100 days that would give all Americans the option to enroll in the government health insurance plan.

Warren's timeline envisions a progression that would initially retain many aspects of the current system, including employer-based private insurance, while transitioning Americans to the government's Medicare health insurance plan that currently covers individuals 65 and older.

The proposal could help blunt criticism, including from a number of the Massachusetts U.S. senator's Democratic presidential rivals, that her Medicare for All plan is too disruptive.

"By the end of my first 100 days, we will have opened the door for tens of millions of Americans to get high-quality Medicare for All coverage at little or no cost. But I won't stop there," Warren wrote on the website Medium.

In the crowded field vying for the Democratic Party's nomination to take on President Donald Trump in November 2020, Warren and progressive rival U.S. Senator Bernie Sanders argue the best route to cover millions of uninsured Americans and lower costs is to replace private insurance with Medicare for All.

Moderate candidates such as former Vice President Joe Biden and Pete Buttigieg, the mayor of South Bend, Indiana, support expanding the Affordable Care Act, while retaining forms of private insurance.

In an acknowledgement of the steep road her proposal would face in Congress if she were elected, Warren said she would use a Senate procedural tactic to pass the first phase, requiring a simple 51-vote majority instead of the usual 60 votes.

Such a move would likely hinge on Democrats regaining control of the Senate, where Republicans currently hold 53 seats in the 100-seat chamber. Democrats control the U.S. House of Representatives, although all 435 seats will also be on ballots in 2020.

Warren's first phase would lower the Medicare eligibility age to 50, offer other Americans the choice to buy into the government program, and provide coverage for children and low-income families.

By the third year, Warren said, she would pass Medicare for All legislation that would allow only "supplemental private insurance that doesn't duplicate the benefits of Medicare for All."

Biden's campaign said it "doesn't change the reality that Medicare for All will deny Americans the right to choose their insurance."

Buttigieg's campaign said it would "eradicate choice."

Warren's transition plan comes two weeks after she released a detailed proposal to pay for a Medicare for All system her campaign estimates would cost $20.5 trillion in additional government spending over a decade.