WASHINGTON — A lawyer for former President Donald J. Trump urged a federal appeals court to quash a congressional subpoena seeking years of financial records from his accounting firm, arguing on Monday that the demand is too broad and could open the door for lawmakers to routinely harass and intimidate future presidents.

“No prior Congress has demanded this kind of information, but every future Congress will if this court upholds the subpoena,” said the lawyer, Cameron T. Norris. “There’s no principled way to limit the fallout to President Trump.”

But Douglas Letter, a lawyer for the House of Representatives, urged the appeals court to uphold the subpoena — including removing limits placed upon it by a district court judge in August. He argued that the subpoena was well within the authority of Congress, especially since the House reissued it after Mr. Trump left office.

“The Constitution does draw a clear line between a president and an ex-president,” Mr. Letter said. “An ex-president is somebody who rejoins the great unwashed.”

Those dueling views in the long-running case, which reached the Supreme Court in 2020 and was sent back down to lower courts to be heard again using a tighter legal standard, were on display on Monday during a nearly two-hour oral argument before a three-judge panel of the United States Court of Appeals for the District of Columbia.

Questions asked by the judges — Ketanji Brown Jackson, Judith W. Rogers and Sri Srinivasan — gave little indication that they were likely to quash the subpoena. But the judges spent extensive time exploring whether there was a basis to narrow the scope of the subpoena, such as by reducing some of the years of files Congress has sought, and if so where to draw the line.

In August, a federal trial judge, Amit P. Mehta of the Federal District Court for the District of Columbia, delivered a split decision in his own second look at the matter. He ruled that Congress could obtain certain records dating back to 2011 but other financial records only as far back as 2017, when Mr. Trump took office.

But both sides appealed Judge Mehta’s ruling. All three judges on the appellate panel were randomly assigned to hear the case and were appointed by Democratic presidents, as was Judge Mehta. But the case appears destined to return to the Supreme Court, which is now controlled by a six-member conservative bloc of Republican appointees.

The congressional oversight investigation grew out of Mr. Trump’s refusal to make his tax returns public when he ran for president and, once he was in office, his decision not to divest his business dealings or place them into a blind trust while he was president.

In early 2019, after Democrats took over the House, the Oversight and Reform Committee issued a subpoena for the records from his accounting firm, Mazars USA, dating back to 2011 and separately requested copies of his tax returns from the Treasury Department.

The committee has said it is exploring whether and how to overhaul laws about financial disclosures by presidents; rules against presidents taking “emoluments,” or payments, especially from foreign governments; and standards for when presidents lease property from the federal government — like Mr. Trump’s leasing of the Old Post Office building in Washington, the site of the Trump International Hotel.

Mr. Trump has fought both efforts, including by filing a lawsuit against Mazars USA to block it from complying with the subpoena. While the Supreme Court eventually permitted the Manhattan district attorney’s office to obtain similar records, the litigation has thus far prevented Congress from seeing them.

Instead, the Supreme Court instructed lower courts to take another look based on a four-part test, including such factors as whether Congress could get the information elsewhere and whether the subpoena is no broader than necessary to meet a legislative objective.

One of the open questions is whether that so-called Mazars test is the standard by which the reissued subpoena should be assessed now that Mr. Trump is out of office. Mr. Norris argued that it should be since it is the same as the version issued while Mr. Trump was president.

Mr. Letter argued that the subpoena met the heightened test, but also said that it no longer applied since Mr. Trump was back among the “great unwashed” of the rest of Americans.

Hanging over the case is the issue of delay. Both in office and out, Mr. Trump has pursued a strategy of using the generally slow pace of litigation to run out the clock on congressional oversight efforts. The briefings and arguments scheduled for this round before the appeals court have already consumed four months since the appeal was docketed in mid-August.

Against that backdrop, Mr. Letter opened by urging the panel to move expeditiously “so the Oversight Committee has the ability to carry out its responsibilities.”

“We urge this court in the strongest possible terms to rule as quickly as possible,” Mr. Letter said.