By Natalie Andrews and Kristina Peterson 

WASHINGTON -- Lawmakers prepared to vote Friday on a weeklong spending bill needed to avoid a shutdown of the U.S. government on Saturday, but Democratic resistance added uncertainty and volatility to the day.

In a related development, Republicans signaled late Thursday that they were still short of the votes needed to revive and pass legislation to replace most of the Affordable Care Act.

House GOP leaders had been trying to corral votes in hopes of passing the bill before President Donald Trump's 100th day in office on Saturday. But House Majority Leader Kevin McCarthy (R., Calif.) said Thursday night that the chamber wouldn't vote on the bill Friday or Saturday.

The developments showed the difficulty GOP leaders have faced in trying to come to terms with Democrats on a spending bill to keep the government open after Friday while also pressing forward on a health-care bill uniformly opposed by Democrats.

With the government's funding set to expire Saturday at 12:01 a.m. ET, Republican leaders have prepared a weeklong stopgap measure that would give lawmakers more time to settle on a spending bill to fund the government through the end of the fiscal year on Sept. 30.

The most contentious issues appear to have been resolved, but Democrats are still trying to block some Republican policy measures. House Democrats have concerns about the five-month spending bill, aides said late Thursday.

Mr. McCarthy said Republicans might have to pass the stopgap bill without Democratic support. That could pose a risk to the bill's passage, given that Democratic votes have often been needed for government spending bills.

Some House Democrats had threatened to oppose the bill Friday if House Republican leaders also brought up their health-care bill for a vote this week. That bill would repeal much of the 2010 health law, championed by Democrats, and replace it with conservative policy.

While GOP leaders have gotten closer to marshaling the votes needed to pass the health-care bill, a significant number of centrist Republicans remain opposed or undecided on the bill.

"If Republicans pursue this partisan path of forcing Americans to pay more for less and destabilizing our country's health-care system...Republicans should be prepared to pass a one-week continuing resolution on their own," House Minority Whip Steny Hoyer (D., Md.) said Thursday.

The Senate has also been expected to act on the short-term spending measure before the Saturday deadline, but Sen. Chuck Schumer of New York, the chamber's Democratic leader, signaled Thursday evening that members of his party weren't ready to sign off on the legislation.

Negotiations on the five-month spending bill could nonetheless wrap up quickly, easing passage of the stopgap measure.

Lawmakers said they hoped to pass a spending bill next week for the rest of the fiscal year. Lawmakers from both parties said they are trying to avoid a government shutdown and that the one-week measure is needed because negotiators ran out of time to finish some narrow pieces of the five-month spending bill before the Saturday deadline.

"They were close, but [there was] not enough time to get it published, and so that's what necessitated the five-day" measure, said Rep. Steve Womack (R., Ark.), a member of the House Appropriations Committee.

The spending bill is expected to increase funding for the military and border security, measures both Republicans and Democrats have signaled they would support.

President Donald Trump placed the blame on Democrats for failing to get to a final deal, posting several tweets Thursday morning.

"I promise to rebuild our military and secure our border. Democrats want to shut down the government. Politics!" he wrote.

In the House, Democratic votes will be needed to pass the five-month spending bill because some conservative members of the Republican majority are expected to oppose it. Democratic votes will also be needed in the Senate, where the bill requires 60 votes to pass; there are 52 Republican senators.

A hurdle was cleared Wednesday, as White House Chief of Staff Reince Priebus told Rep. Nancy Pelosi of California, the House Democratic leader, that the administration would continue making "cost-sharing reduction" payments to health insurers, despite the lack of an appropriation for them in the April spending bill.

The assurance appeared to satisfy Democrats, who have warned that insurers would stop offering policies under the Affordable Care Act if the payments ended.

The stopgap resolution would also extend health-care coverage by one week for more than 22,000 retired coal miners and their dependents who are facing a loss of care with the government deadline. Lawmakers are wrangling over whether to extend the funding permanently or on a more limited basis.

Write to Natalie Andrews at Natalie.Andrews@wsj.com and Kristina Peterson at kristina.peterson@wsj.com

(END) Dow Jones Newswires

April 27, 2017 23:40 ET (03:40 GMT)

Copyright (c) 2017 Dow Jones & Company, Inc.