WASHINGTON — Top Trump administration officials have pushed to build nuclear power plants throughout Saudi Arabia over the vigorous objections of White House lawyers who question the legality of the plan and the ethics of a venture that could enrich Trump allies, according to a new report by House Democrats released on Tuesday.

The report is the most detailed portrait to date of how senior White House figures — including Michael T. Flynn, President Trump’s first national security adviser — worked with retired military officers to circumvent the normal policy making process to promote an export plan that experts worried could spread nuclear weapons technology in the volatile Middle East. Administration lawyers warned that the nuclear exports plan — called the Middle East Marshall Plan — could violate laws meant to stop nuclear proliferation and raised concerns about Mr. Flynn’s conflicts of interest.

Mr. Flynn had worked on the issue for the company promoting the nuclear export plan and kept pushing it once inside the White House.

But even after Mr. Flynn was fired, the proposal appears to have lingered. The initial discussions took place during the chaotic early months of the Trump administration, according to the 24-page report from the House Oversight and Reform Committee, but House Democrats on Tuesday cited evidence that as recently as last week the White House was still considering some version of the proposal. Democrats said they had begun a full-scale inquiry.

“Further investigation is needed to determine whether the actions being pursued by the Trump administration are in the national security interest of the United States or, rather, serve those who stand to gain financially as a result of this potential change in U.S. foreign policy,” committee staff wrote in the report.

The Trump administration’s relationship with Saudi Arabia has already been examined by federal investigators, including the special counsel, Robert S. Mueller III. But House Democrats could expand the inquiry into whether the prospect of business deals might have had a direct effect on American foreign policy in the oil-rich Persian Gulf region.

In this case, it was American nuclear energy companies and the retired generals and other former government officials working with them who stood to benefit financially if the federal government signed off on IP3’s proposal for building of the nuclear power sites.

The White House did not respond to a request for comment, and a lawyer for Mr. Flynn did not respond to a message seeking comment.

Claims presented by whistle-blowers and White House documents obtained by the House oversight committee show that the company backing the nuclear plan, IP3 International, was working so closely with allies in the Trump political world that the company sent draft memos that would be needed from the president for the nuclear export plan to Mr. Flynn just days after Mr. Trump took office.

A week after Inauguration Day, the Democrats’ report said, a Flynn deputy for Middle East and North African affairs, Derek Harvey, met with the IP3’s co-founders at the White House, and asked National Security Council staff to include information about the nuclear power plan in a briefing to prepare Mr. Trump for a call with King Salman of Saudi Arabia.

The speed with which Mr. Harvey acted, and his circumvention of the normal scrutiny by experts across the government — like officials in the Energy and State Departments — prompted at least some National Security Council officials to raise concerns with Mr. Harvey, the report said. Eventually, ethics lawyers also raised concerns.

Even after Mr. Flynn left the White House in February 2017 under scrutiny by the F.B.I. for his communications with Russia, officials on the National Security Council continued to push ahead, repeatedly ignoring advice from the council’s ethics counsel, the report said.

At a March 2017 meeting, Mr. Harvey tried to revive the IP3 plan “so that Jared Kushner can present it to the president for approval,” the Democratic report said, a reference to Mr. Trump’s son-in-law and top adviser. Eventually Mr. Flynn’s successor, H. R. McMaster, said all work on the plan should cease because of potentially illegal conflicts.

The draft memos sent by IP3 to Mr. Flynn also referenced another close Trump associate, Thomas J. Barrack Jr., a businessman with deep ties to the Middle East who served as chairman of the president’s inaugural committee. In one memo from Mr. Flynn to Mr. Trump, the national security adviser advocated that Mr. Barrack be named a special representative to carry out the nuclear plan. Another memo, written as if it was from Mr. Trump to cabinet secretaries and other military and intelligence officials, directed federal agencies to support Mr. Barrack’s efforts.

The Democrats’ investigation comes at a sensitive time, when lawmakers of both parties are incensed over the Trump administration’s reluctance to punish Prince Mohammed bin Salman and the Saudi government over the killing of the Washington Post journalist Jamal Khashoggi. As supporters of the nuclear deal maneuvered in the opening days of the Trump White House, Mr. Kushner was orchestrating what would be Mr. Trump’s first overseas trip as president, to Saudi Arabia, and met on his own with the deputy crown prince at the time, Mr. bin Salman, before the prince became the power behind the Saudi throne.

Mr. Kushner’s efforts continue. He is scheduled to travel to the region next week, with a stop in Riyadh, the Saudi capital, to brief diplomats on the economic portions of the Trump administration’s Middle East peace plan.

The special counsel’s investigation has spent months examining contacts between Trump advisers and both officials and informal emissaries from Saudi Arabia and the United Arab Emirates. Prosecutors have been trying to determine whether the gulf monarchies might have spent money to try to influence Mr. Trump’s political activities, including his 2016 presidential campaign.

Prosecutors at one point were particularly focused on what business interests might have been discussed in meetings leading up to the 2017 Riyadh summit meeting, according to people familiar with the witness interviews.

Representative Elijah E. Cummings of Maryland, raised alarms on the nuclear exports in 2017 when he disclosed claims brought to him by a whistle-blower. But the committee’s Republican chairman at the time did nothing.

So on Tuesday, Mr. Cummings, now the committee’s chairman, said he would do the work himself.

Republicans on the committee did not receive a copy of the report until last night and had not fully assessed it, according to their spokeswoman, Charli Huddleston.

“This is a delicate and nuanced issue that Chairman Cummings is approaching without bipartisan input and with far-flung requests for information,” she said.

In a statement, a spokesman for Mr. Barrack said that he would cooperate with Mr. Cummings’s investigation and noted he had never taken a job in the administration.

In an unsigned statement, IP3 said that it would cooperate with Mr. Cummings’s inquiry and that Mr. Flynn had no financial stake in the company. It defended its plan at length, framing it as a matter of “vital national security interest” for the United States to compete with foreign competitors like Russia and China who are seeking to grow their influence in the region.

“Only the United States nuclear industry can deliver the standard of safety, security, regulatory oversight and operational primacy required to ensure both the nonproliferation goals as well as the strategic goals of the United States are achieved,” the statement said. “Achieving these goals will require close coordination between the U.S. government and industry.”

Jack Langer, a spokesman for Republicans on the House Intelligence Committee, where Mr. Harvey now works, called the details about him “a ridiculous conspiracy theory.”

The export of American nuclear technology that could be used to create nuclear weapons is strictly controlled under the Atomic Energy Act of 1954. The act says that Congress must approve such exports, and at least one of the whistle-blowers that went to the Democrats claimed that officials involved ignored warnings about such legal requirements.

A plan like the one advocated by IP3 International has not gone forward to date. But Mr. Cummings’s staff said there was evidence that the White House was still kicking around the proposal.

Mr. Trump met with nuclear industry executives at the White House last week to discuss expanding their presence internationally, including in the Middle East. Bloomberg reported that the session was organized by Jack Keane, a retired four-star Army general and one of the founders of IP3 International.

The IP3 project was the second nuclear power plan that Mr. Flynn had worked on, according to people involved in the projects. During 2015 and 2016, after he retired from the military, Mr. Flynn had consulted with and traveled to the Middle East on behalf of ACU Strategic Partners, which was pursuing an ambitious plan that envisioned Russia taking spent nuclear fuel to avoid the danger of nuclear proliferation.

Some of the retired generals who advised the ACU Strategic Partners effort subsequently broke off and created IP3, which for a time argued for replacing Russia with China in the nuclear power plan.