* Trump to meet with Democratic leaders Pelosi, Schumer
* He touts 'biggest' tax cut, reform package in U.S. history (Adds Trump meeting with Democratic congressional leaders Pelosi, Schumer, Ryan comments on deficit-neutral tax cut)
WASHINGTON, Sept 13 (Reuters) - U.S. President Donald Trump on Wednesday stepped up his outreach to Democrats to try to make good on a campaign promise for major tax cuts, while fellow Republicans in the House of Representatives promised an outline of a tax plan in two weeks.
The White House and the Republican-led Congress have not put forth a detailed tax plan despite months of talks. House Speaker Paul Ryan said an outline will be unveiled during the work week beginning Sept. 25, with the House tax-writing committees then crafting legislation in the subsequent weeks.
"It's the beginning of a very important process to achieve for the first time in a generation overhauling our tax system and giving middle-class families a much deserved break," Ryan told reporters.
As Trump continues to seek Democratic input on the tax front, he was set to meet on Wednesday afternoon at the White House with House members, including eight Democrats and five Republicans.
Trump also invited Senate Democratic Leader Chuck Schumer and House Democratic Leader Nancy Pelosi to dine with him on Wednesday night, Democratic sources familiar with the matter said.
Trump last week blindsided Republican leaders by striking a deal with Schumer and Pelosi on the U.S. debt limit and federal spending for three months, and also spoke to them about how to resolve the fate of 800,000 young adults brought into the United States illegally as children, the so-called Dreamers.
The White House said Trump's meeting with seven senators, including three Democrats, on Tuesday night on taxes was "highly productive" and would "spur constructive discussion."
Trump went to Twitter to urge Congress to "move fast" on what he called "the biggest Tax Cut & Tax Reform package in the history of our country." He also tweeted that the tax measure "is needed more than ever" after the damage caused by hurricanes Irma and Harvey.
Republicans have been trying for most of the year to come up with a detailed tax plan while ignoring the Democrats. There has been no comprehensive overhaul of the U.S. tax code since 1986, and the starkly different visions embraced by the two parties for how to move forward promise to make the task difficult.
Republicans are advocating a deep cut in the corporate tax rate, tax cuts for the middle class and a simplified code. But Democrats, emphasizing the need for relief for the middle class, have criticized the Republican efforts as benefiting mainly the wealthiest Americans.
Ryan said the outline being worked on now would reflect the consensus of the House Ways and Means Committee, Finance Committee and the Trump administration.
"I would love to have the Democrats supporting and working with us in a constructive way on tax reform, but we're going to do it no matter what," Ryan said.
Ryan, in an interview with the Associated Press, left the door open on whether the tax proposal would increase the U.S. deficit or follow Republicans' long-standing principle that the cost of any legislation be offset by government spending cuts.
Ryan and Treasury Secretary Steven Mnuchin last week expressed confidence that Congress will pass the tax legislation this year. Both have cast doubt on the likelihood that the plan would realize Trump's goal of cutting the corporate tax rate from the current 35 to 15 percent.
In his nearly eight months in office, Trump has failed to get his major legislative goals through Congress. A bid to dismantle the Obamacare healthcare law fell apart and he has not unveiled detailed proposals on taxes and infrastructure spending.
Democrats largely have lined up against Trump's legislative priorities, but he has shown a newfound willingness to work across party lines.
Democratic aides said Schumer and Pelosi will press Trump on Wednesday evening for action to protect the Dreamers after the president rescinded a five-year-old program to spare them from deportation, and to stabilize health insurance markets under Obamacare.
Democrat Joe Manchin, one of the senators who met with Trump on Tuesday, told CBS News that Trump was "very aggressive" on the need for a bipartisan plan.
"The president comes out right away and says, 'Listen, this is not a tax cut for the rich. I'm not going to get a tax cut, nor any of the wealthy, super one-percenters will get any tax cuts,"' said Manchin, saying he is "anxious" to see a template of the plan. (Reporting by Roberta Rampton and Susan Cornwell; Additional reporting by Makini Brice, Richard Cowan, David Morgan and Susan Heavey; Writing by Will Dunham; Editing by Frances Kerry and Alistair Bell)