WASHINGTON (REUTERS) - Republican negotiators in the US Congress put the finishing touches on a sweeping tax overhaul and will release the details later on Friday (Dec 15), including plans for an expanded child tax credit aimed at winning the support of two wavering senators.

Representative Kevin Brady, chairman of the tax-writing House Ways and Means Committee, told reporters that Republican negotiators on a House-Senate committee working on the Bill had signed the finished product and the details would be published when the full House convenes at 5.30pm EST (6.30am on Saturday, Singapore time).

One of the negotiators, Republican Representative Kristi Noem, said the refundable portion of an expanded child tax credit in the revamped Bill rises to US$1,400 (S$1,800) from US$1,000, an apparent bid to win support from Republican Senators Marco Rubio and Mike Lee.

The two lawmakers had criticised an earlier draft of the Bill for making only about half of the credit refundable. Rubio later signaled he was ready to support the revamped tax package after the changes.

"Increasing the refundability of the Child Tax Credit from 55 per cent to 70 per cent is a solid step toward broader reforms which are both Pro-Growth and Pro-Worker," Rubio said on Twitter.

The completion of the tax overhaul clears the way for final votes in the full House and Senate next week. President Donald Trump, who touted a tax cut constantly during his campaign, wants an approved Bill on his desk for his signature before Christmas.

It would be Trump's first major legislative victory since taking office in January.

With all 46 Democrats and two independents in opposition to the measure, Republicans can only afford to lose two of their 52 senators and still win passage. Republican Senator Bob Corker opposed an earlier version of the legislation, largely because of the Bill's impact on federal deficits.

HURDLES REMAIN

As the tax package has evolved, it has tilted increasingly towards benefiting businesses and the wealthy, a trend some lawmakers have said is a concern. Provisions for offsetting the revenue costs of last-minute changes also were troublesome for some lawmakers.

After resisting demands for weeks to cut the top income tax rate for the richest taxpayers, the Bill's authors did agree in recent days to lower it to 37 per cent from 39.6 per cent.

The Senate approved a wide-ranging version of the tax Bill on Dec 2 by a vote of 51-49, with Corker the only Republican to vote no. Earlier, the House of Representatives had approved its own tax legislation.

Independent and nonpartisan tax analysts have estimated that the Bill will expand the US$20 trillion national debt by at least US$1 trillion in the next 10 years.

Moderate Republican Senator Susan Collins also has been non-committal on the Bill, in part out of concern about its provision to repeal an Obamacare federal fine imposed on Americans who do not buy health insurance.

The Senate vote outlook has been further muddled by Senator John McCain's admission to the hospital for treatment for side effects of cancer therapy. His office said he "looks forward to returning to work as soon as possible."

Vice-President Mike Pence has delayed a planned trip to the Middle East in case his vote is needed to break a tie on the final tax Bill.