WASHINGTON — The Trump administration claimed victory on Tuesday in its crackdown on illegal immigration during its first several months, announcing that the number of arrests at the border dropped to the lowest in nearly a half-century as proof that its deterrence efforts have been effective.

Border Patrol agents arrested 310,531 people trying to enter the country illegally during the fiscal year that ended Sept. 30, a 25 percent decrease from the previous fiscal year. About one-third were from Mexico, according to the Border Patrol. Most of the rest were from El Salvador, Guatemala and Honduras.

Inside the United States, officials at Immigration and Customs Enforcement also arrested 143,470 people, a 25 percent increase over the previous fiscal year, officials at the Department of Homeland Security said. The increase comes after the Trump administration reversed an Obama-era policy that only targeted those with criminal records.

“We have clearly seen the successful results of the president’s commitment to supporting the front-line officers and agents of D.H.S. as they enforce the law and secure our borders,” said Elaine C. Duke, the acting Homeland Security secretary.