WASHINGTON — The Department of Veterans Affairs warned Wednesday it was unexpectedly running out of money for a program that offers veterans private-sector health care, forcing it to hold back on some services that lawmakers worry could delay medical treatment.

It is making an urgent request to Congress to allow it to shift money from other programs to fill the sudden budget gap.

VA Secretary David Shulkin made the surprising revelation at a Senate hearing. He cited a shortfall of more than $1 billion in the Choice program due to increased demand from veterans for federally-paid medical care outside the VA. The VA had previously assured Congress that funding for Choice would last until early next year.

“We need your help on the best solution to get more money into the Choice account,” Shulkin told the Senate Veterans’ Affairs Committee. “If there is no action at all by Congress, then the Choice program will dry up by mid-August.”

The department began instructing VA medical centers late last week to limit the number of veterans it sent to private doctors so it can slow spending in the Choice account. Some veterans were being sent to Defense Department hospitals, VA facilities located farther away, or other alternative locations “when care is not offered in VA,” according to a June 7 internal VA memorandum.

The VA is also scrambling to tap other parts of its budget, including about $620 million in carry-over money that it had set aside for use in the next fiscal year beginning Oct. 1. It was asking field offices to hold off on spending for certain medical equipment to help cover costs, according to a call the department held with several congressional committees Tuesday night.

It did not rule out taking money from VA hospitals.

Shulkin on Wednesday insisted that veterans will not see an impact in their health care. He blamed in part the department’s excessive use of an exception in the Choice program that allowed veterans to go to private doctors if they faced an “excessive burden” in traveling to a VA facility. Typically, Choice restricts use of private doctors only when veterans must wait 30 days or more for an appointment or drive more than 40 miles to a facility.