By Ted Hesson and Mica Rosenberg

WASHINGTON (Reuters) - A U.S. appeals court on Monday sided with President Donald Trump over his administration's decision to end humanitarian protections for hundreds of thousands of immigrants, many of whom have lived in the United States for decades.

In a 2-1 ruling, a panel of three judges in the California-based U.S. 9th Circuit Court of Appeals reversed a lower court decision that had blocked Trump's move to phase out so-called Temporary Protected Status (TPS) for people from El Salvador, Haiti, Nicaragua and Sudan.

The ruling is also expected to affect the status of people from Honduras and Nepal, who filed a separate lawsuit that was suspended last year pending the outcome of the broader case.

The TPS enrollees from the six countries currently have work authorization through Jan. 4, 2021. The appeals court ruling means that those immigrants will be required to find another way to remain in the United States legally or depart after a wind-down period of at least six months and longer in the case of El Salvador. However, the case is likely to be appealed to the U.S. Supreme Court, which could delay that outcome.

The termination of TPS for Haitians is also subject to separate litigation in the U.S. 2nd Circuit Court of Appeals in New York.

Trump has made his tough immigration stance a hallmark of his presidency and 2020 re-election campaign against Democratic challenger Joe Biden.

TPS allows foreigners whose home countries experience a natural disaster, armed conflict or other extraordinary event to remain in the United States and apply for work permits. The status must be renewed periodically by the secretary of homeland security, who can extend it for six- to 18-month intervals.

The Trump administration has argued that most countries in the program have recovered from the related disasters or conflicts, while the status has been renewed for years beyond its need.

Immigrants from El Salvador make up the largest group of TPS recipients, with an estimated 263,000 Salvadorans covered by the program, but a bilateral agreement will allow Salvadorans an additional year to stay in the United States if the courts ultimately uphold Trump's termination.