(Adds Trump to propose initial $5.9 billion in aid)

By Susan Cornwell and David Morgan

WASHINGTON, Aug 31 (Reuters) - Estimates of the size of a Hurricane Harvey aid package for Texas and Louisiana rose on Thursday, with one proposal being drafted for $150 billion, while the White House promised to make a request for funding soon to Congress.

The Trump administration will make a request to the U.S. Congress shortly for funds to help recovery efforts from Harvey, which caused devastating flooding, White House homeland security adviser Tom Bossert said.

He told reporters that an aid funding request will likely come in stages as more is known about the storm's impact.

Trump has prepared a request to Congress for an initial $5.9 billion in aid, an administration official said.

U.S. taxpayers are likely to face a bill for Harvey near the $110.2 billion for 2005's Hurricane Katrina. Estimates on the amount of the Harvey aid varied widely.

Representative Sheila Jackson Lee, a Democrat from Houston, was crafting legislation for $150 billion in emergency funding through nearly two-dozen government agencies and departments.

Texas Governor Greg Abbott said on Wednesday the state could need more than $125 billion.

Figures of $50 billion to $80 billion were cited by Republican Representatives Pete Sessions of Texas and Leonard Lance of New Jersey on Fox Business Network.

The Federal Emergency Management Agency's disaster relief fund had only $3.3 billion when the storm struck.

A Republican leadership source said Congress was expected to consider and vote on an initial allocation of Harvey aid in the first half of September.

IMPACT ON BROADER GOVERNMENT FUNDING ISSUE

The urgency of aiding areas hit by Harvey may also complicate a broader fiscal policy showdown that is coming in late September.

When Harvey plowed into the Texas coast this week, Congress and President Donald Trump were already struggling to deal with the debt ceiling, which is a cap on how much money the federal government can borrow, and the need to approve a temporary federal budget bill by Oct. 1 to prevent a government shutdown.

Treasury Secretary Steven Mnuchin told broadcaster CNBC on Thursday that the impact of Hurricane Harvey spending could bring forward the deadline by which the nation's debt ceiling needs to be raised by "a couple of days." He repeated that the limit needs to be raised by Sept. 29

Financial markets have been anxious about the possibility of the debt ceiling not being raised, which could cause a U.S. credit default and send economic shockwaves worldwide.