WASHINGTON — The White House has rebuffed concerns among American intelligence and law enforcement officials and ordered that more lawmakers be given access to classified information about an informant the F.B.I. used in 2016 to investigate possible ties between the Trump campaign and Russia, according to two American officials with knowledge of the decision.
Both the director of national intelligence and the director of the F.B.I. tried to keep the classified documents tightly restricted, fearing that a broader dissemination of operational reports and other sensitive material could lead to more leaks of detailed information about the role of the confidential F.B.I. informant.
Some American officials believe, in fact, the reason the White House made the decision was to provide political ammunition to President Trump’s Republican allies who have argued — without any evidence — that the F.B.I. investigation was opened in July 2016 as an effort to keep Mr. Trump from becoming president.
The F.B.I. files about the informant will now be available to all members of the Senate and House Intelligence Committees, instead of to just a group of congressional leaders known as the Gang of Eight. It is unclear whether Mr. Trump or a lower-level White House official authorized the move.
The controversy over the F.B.I. informant is one skirmish in a searing political battle that was renewed on Thursday during a contentious hearing convened by the House Judiciary and Oversight Committees that heard testimony from Peter Strzok, an F.B.I. agent who once ran the bureau’s investigation into the Trump campaign.
During the summer of 2016, the F.B.I. sent an informant to meet with two Trump campaign advisers after the bureau had received information that the two men had suspicious contacts linked to Russia. The informant, Stefan Halper, an American academic who teaches at Cambridge University in England, had meetings with both Carter Page and George Papadopoulos to gain a better understanding of their contacts with Russians.
The New York Times did not originally name Mr. Halper because of a general practice not to name confidential F.B.I. informants to preserve their safety. Mr. Halper’s name has now been widely reported.
A veteran of several Republican administrations, Mr. Halper has been a source of information to the C.I.A. and other American security agencies for several years, according to people familiar with his work for the government.
F.B.I. officials concluded that they had the legal authority to open the investigation into the Trump campaign after they received information that Mr. Papadopoulos had been told that the Russians had compromising information about Hillary Clinton, the Democratic presidential candidate, in the form of “thousands of emails,” months before WikiLeaks released stolen messages from Democratic officials.
Mr. Trump’s congressional allies reacted angrily to the revelation of Mr. Halper’s role in the F.B.I. investigation, accusing the bureau of “spying” on the Trump campaign. The president himself has called the issue a “scandal” on Twitter.
“Reports are there was indeed at least one FBI representative implanted, for political purposes, into my campaign for president,” he wrote in May.
“If true — all time biggest political scandal!”
Congressional leaders have received two briefings about Mr. Halper’s role in the F.B.I. investigation. One of the briefings was attended by John F. Kelly, the White House chief of staff, and Emmet T. Flood, a White House lawyer handling issues related to the special counsel’s Russia investigation — leading to vocal criticism on Capitol Hill that it was improper for White House officials to attend a classified briefing about an investigation that involves the president.
Representative Devin Nunes of California, the chairman of the House Intelligence Committee and one of the president’s staunchest defenders in Congress, for weeks has demanded that the full House and Senate Intelligence Committees be given access to documents about the informant’s role in the campaign. He has accused the Justice Department of “obstruction” of a congressional investigation.
Democrats have argued that the true aim of the Republicans is to undermine the Russia investigation — which in May 2017 was taken over by the special counsel, Robert S. Mueller III — and that Republicans want access to F.B.I. files to gain information they can use against the inquiry.
Intelligence and law enforcement officials — including Dan Coats, the director of national intelligence, and Christopher A. Wray, the F.B.I. director — were opposed to expanding the number of lawmakers who can read the classified files, according to people with knowledge of their thinking.
In a letter to Mr. Coats on Thursday, Democratic members of the Gang of Eight protested the release of the documents, saying that it “contravenes your representation to us and our colleagues that this information would not be shared outside that group.”
“We believe your decision could put sources and methods at risk,” they added.
Representatives for the F.B.I. and the director of national intelligence declined to comment. The White House did not respond to a request for comment.
During congressional testimony in May, Mr. Wray gave a thinly veiled warning to lawmakers about the dangers of exposing information about confidential sources.
“The day that we can’t protect human sources is the day the American people start becoming less safe,” he said.