WASHINGTON >> The Supreme Court on Monday seemed likely to expand presidential control over independent federal agencies, signaling support for President Donald Trump’s firing of board members.

The court’s conservative majority suggested it would overturn a unanimous 90-year-old decision that has limited when presidents can fire agencies’ board members — in part to try to ensure decision making free of political influence — or leave it with only its shell intact.

Justice Brett Kavanaugh said the crux of the issue is that the officials who direct the agencies “are exercising massive power over individual liberty and billion-dollar industries” without being accountable to anyone.

Liberal justices warned that a ruling sought by the administration to overturn the decision known as Humphrey’s Executor would give the president, as Justice Elena Kagan said, “massive unchecked, uncontrolled power.”

Agencies that have been in place for a century or more also would be robbed of their expertise, Justice Ketanji Brown Jackson said.

“So having a President come in and fire all the scientists and the doctors and the economists and the PhDs and replacing them with loyalists and people who don’t know anything is actually not in the best interest of the citizens of the United States,” Jackson said.

No president before Trump has sought to wrest control of the agencies that regulate wide swaths of American life. But the six conservatives, including three appointed by Trump, seemed more concerned about issuing a ruling that would endure than handing too much power to Trump.

Solicitor General D. John Sauer, who argued the immunity case for Trump, defended the president’s decision to fire Federal Trade Commission member Rebecca Slaughter without cause and called on the court to jettison Humphrey’s Executor.

Sauer said the decision “hasn’t withstood the test of time” and had enabled a “headless fourth branch” of government, the administrative state.

The conservative side of the court already has signaled support for the administration’s position, over the liberals’ objection, by allowing Slaughter and the board members of other agencies to be removed from their jobs even as their legal challenges continue.

Members of the National Labor Relations Board, the Merit Systems Protection Board and the Consumer Product Safety Commission also have been fired by Trump.

The only officials who have so far survived efforts to remove them are Lisa Cook, a Federal Reserve governor, and Shira Perlmutter, a copyright official with the Library of Congress.