* Measure to seek up to $6 trillion in tax cuts
* Republican leaders to meet with Trump on Thursday
* Democrat Pelosi says Republicans pushing "half-baked" bill (Adds Brady, Trump, Pelosi, Zeldin, Sanders comments, bill details)
WASHINGTON, Nov 1 (Reuters) - A tax bill offering plenty of flexibility was expected to be released by Republicans in the U.S. House of Representatives on Thursday as they grapple with stubborn internal disagreements on paying for the tax cuts they propose.
After an embarrassing one-day postponement of the bill's unveiling on Wednesday, lawmakers have made plans for a measure that will seek up to $6 trillion in tax cuts over 10 years but likely not spell out completely how to offset them.
On the Republican proposal to slash the corporate tax rate to 20 percent from 35 percent, U.S. House of Representatives tax panel Chairman Kevin Brady said on Wednesday: "That's our goal and I think it's going to take several steps ... to achieve that."
At the White House after a meeting with advisers, President Donald Trump told reporters: "Sometime tomorrow, we'll be announcing massive tax cuts and reform."
House Republican leaders and tax panel members were slated to meet with Trump in the White House on Thursday afternoon.
From mortgage interest and 401(k) retirement plans to the federal deficit and state and local taxes, numerous unanswered questions swirled around the tax-cut plan as lawmakers met into the evening on Capitol Hill.
Representative Tom MacArthur, asked if fellow Republicans could meet their ambitious deadline of approving a tax bill by the Nov. 23 Thanksgiving holiday, told reporters: "I've been called a lot of things but 'prophet' is not one of them."
Since taking over Congress and the White House in January, the Republicans and Trump have yet to score a major legislative accomplishment. That will change, they say, when they overhaul the tax code for the first time in 31 years.
But they are fast discovering why every attempt to do that has failed since former Republican President Ronald Reagan's historic tax reform in 1986.
Unlike the nearly three-year Reagan effort involving public hearings and bipartisan cooperation, the Trump tax plan was developed in secret over a few months by six senior lawmakers and White House advisers who took little input from rank-and-file Republicans and largely ignored the Democrats.
House Democratic Leader Nancy Pelosi said in a statement that the "chaotic delay" of the tax bill's release showed Republicans were "pushing a half-baked tax bill with ruinous consequences for workers and middle-class Americans."
MacArthur said the plan's biggest challenge was a proposed elimination of a deduction for state and local tax (SALT) payments, which is among several revenue-raising changes meant to offset proposed tax cuts. Other lawmakers and lobbyists cited different concerns with the bill..
Republicans from high-tax states where upper-middle-class voters would be hardest hit by the SALT deduction repeal were unsure if the bill on Thursday would address their concerns.
Representative Lee Zeldin from New York said he wanted major changes to preserve state and local tax deductibility. I was encouraged when I heard Chairman Brady refer to the draft thats about to get released as not being the final text," said Zeldin.
MacArthur, who is from New Jersey, said a compromise proposal being worked on to maintain and cap the deductibility of property tax payments was a good start that but the cap would need to be raised to earn his support for the bill.
Trump, largely playing a cheerleader role in the tax debate, tweeted advice on Twitter on Wednesday on paying for the cuts. "Wouldn't it be great to Repeal the very unfair and unpopular Individual Mandate in ObamaCare and use those savings for further Tax Cuts," he said in a Twitter post on Wednesday.
Afterward, White House spokeswoman Sarah Sanders told reporters in a briefing that the administration still wanted to repeal and replace Obamacare, but "we still think it's probably more likely to do something like that in the spring."
An attempt to dismantle the Affordable Care Act, the healthcare law enacted in 2010 under former Democratic President Barack Obama, failed dramatically in the Republican-controlled Senate in July.
401(k) IN PLAY
Another contentious revenue-raising proposal in the plan is to limit how much money Americans can put into their 401(k) retirement accounts and individual retirement accounts (IRAs) on a pre-tax basis.
There was also a proposal to limit the deductibility of interest payments by businesses. Restrictions are opposed by businesses with little access to equity financing, including farmers, ranchers and small businesses.
A rough framework of the tax plan was unveiled in late September, but its basic components were changing.
It originally called for reducing the number of tax brackets to three from seven, with the current top tax rate of 39.6 percent reduced to 35 percent, a win for high-income taxpayers.
Partly in response to Democrats who dismissed the plan as a giveaway to corporations and the wealthy, lawmakers are expected to restore a fourth, top tax bracket to the bill, but increase the income level where it applies, perhaps to $1 million, more than double the current level.
Questions remained about the original framework's proposal to repeal the estate tax on inheritances, another policy change that would favor wealthy Americans. Discussion was ongoing about possibly phasing that out, Republicans said.
Lawmakers also have not resolved a challenge posed by Trump's plan to lower the tax rate on pass-through enterprises, such as partnerships and sole proprietorships, to 25 percent from as high as 39.6 percent, they said.
(Reporting by David Morgan and Amanda Becker; Editing by Kevin Drawbaugh and Peter Cooney)