(Adds comments by McConnell, Schumer, Graves)
WASHINGTON, Feb 12 (Reuters) - President Donald Trump has not yet decided whether to back an agreement hammered out by congressional negotiators to avert another partial government shutdown that includes funds for U.S.-Mexican border security but not for his promised wall, the White House said on Tuesday.
Democratic and Republican negotiators reached the tentative deal on Monday night on border security provisions and money to keep several government agencies including the Department of Homeland Security funded through Sept. 30, the end of the current fiscal year. Temporary funding for about a quarter of the government is due to expire on Friday.
The Republican president triggered a 35-day partial government shutdown with his December demand for Congress to give him $5.7 billion to help build the border wall, which is opposed by Democrats. At a rally in Texas on Monday night, he made clear he would not drop his quest for a wall.
Trump has not yet made up his mind on the deal reached by lawmakers, said a White House official, speaking on condition of anonymity. "No decision has been made," the official said.
The tentative deal still requires congressional staff experts to write formal legislation, filling in details lacking in the broad outline reached late on Monday. The legislation would need to be passed in the Democratic-led House and Republican-controlled Senate and signed by Trump.
Tom Graves, a House Republican who serves on the congressional conference committee that worked on the border security and other funding, raised questions about the compromise. Graves wrote on Twitter that he had not "signed off on the reported 'deal' nor have I seen it. Based on the reports, I have concerns. Lots of questions too."
Congressional sources said the agreement includes $1.37 billion for new fencing along 55 miles (90 km) of the southern border but only with currently used designs such as "steel bollard" fencing. It also addresses capacity at immigration detention facilities, specifically the number of beds for people awaiting possible deportation.
"I am cautiously optimistic that we will get this through," Democrat Nita Lowey, who chairs the House of Representatives Appropriations Committee, told CNN. "We cannot shut the government down."
Lowey has said the legislation might be written by Wednesday, leaving little time for Congress and pass the measure by Friday's midnight deadline. Lowey said the deal had the backing of House Speaker Nancy Pelosi and other Democrats.
'IN SHORT ORDER'
Senate Majority Leader Mitch McConnell said he hopes his chamber can act on the legislation "in short order," calling the announcement of the agreement in principle "certainly good news."
McConnell said the agreement "provides new funds for miles of new border barriers, and it completes all seven outstanding appropriation bills so Congress can complete a funding process for all the outstanding parts of the federal government with predictability and with certainty."
Top Senate Democrat Chuck Schumer said the parameters of the deal are good and expressed hope that it would avert another shutdown. "I strongly urge the president to sign this," Schumer said.
Trump's long-promised wall was a cornerstone of his presidential campaign. He had said it would be paid for by Mexico and not by U.S. taxpayers.
The president last month agreed to end the shutdown without getting money for a wall, which is opposed by Democrats. The shutdown roiled financial markets and left hundreds of thousands of federal workers and contractors without pay.
Trump will have to decide whether to sign the measure into law given its backing from congressional Republicans, or side with conservative commentators who have the president's ear such as Sean Hannity of Fox News, who late on Monday called it a "garbage compromise." Democrats oppose the wall but support border security efforts.
Trump previously has threatened to declare a "national emergency" if Congress does not provide money specifically for the wall, an action he might take to redirect other funds already provided by Congress instead to pay for wall construction.
"Just so you know - we're building the wall anyway," Trump said at Monday's rally in the border city of Texas.
Beto O'Rourke, the former Democratic congressman from Texas considering a 2020 White House run, accused Trump at a counter-rally nearby of stoking "false fear" about immigrants and telling "lies" about O'Rourke's hometown of El Paso.
Without new funds, federal agencies would again have to suspend some activities this weekend, ranging from maintenance of national parks to the publishing of important economic data.
(Reporting by Richard Cowan; Additional reporting by Susan Cornwell and Steve Holland in Washington and Roberta Rampton in El Paso, Texas; Editing by Will Dunham)