WASHINGTON — The White House and congressional Republicans are finalizing a tax plan that would slash the corporate rate while likely reducing the tax rate for the wealthiest Americans, with President Donald Trump ready to roll out the policy proposal at midweek.

The grand plan to rewrite the nation’s tax code would be the first major overhaul in three decades, delivering on a Trump campaign pledge. It also is expected to eliminate or reduce some tax breaks and deductions.

The plan would likely cut the tax rate for the wealthiest Americans, now at 39.6 percent, to 35 percent, people familiar with the plan said Monday. They spoke on condition of anonymity ahead of a formal announcement.

In addition, the top tax for corporations would be reduced to around 20 percent from the current 35 percent, they said. It will seek to simplify the tax system by reducing the number of income tax brackets from seven to three.

Trump has said he wanted to see a 15 percent rate for corporations, but House Speaker Paul Ryan has called that impractically low and risks adding to the $20 trillion national debt.

The White House and congressional leaders planned an all-out blitz later this week to build support for the plan, now Trump’s top legislative priority as the GOP struggles to repeal and replace the Affordable Care Act.