The chief executive of the state agency that runs New York City’s subway and bus network said on Monday that the agency’s priority would be keeping the aging transit system operating safely now that an ambitious plan to improve it confronts a $15 billion shortfall.

The chief executive, Janno Lieber, said the agency, the Metropolitan Transportation Authority, would emphasize “basic stuff to make sure the system doesn’t fall apart” after Gov. Kathy Hochul’s abrupt move last week to halt a congestion-pricing plan that was to finance capital projects.

Mr. Lieber, speaking at a news conference where he was joined by a group of grim-faced authority executives, said Ms. Hochul’s decision would force the M.T.A. to shrink its current capital budget, and could potentially affect its next budget and even ripple into day-to-day operations.

Among the future projects at risk was the next phase of the Second Avenue Subway line, he said. The authority will now have to scramble to hold onto a $3.2 billion federal grant it had secured to help pay for extending the line.

He also said the authority would “fight like hell” to avoid having to make service cuts that could plunge the city’s transit system into the kind of dysfunction that defined it in the 1970s and ’80s.

Mr. Lieber’s remarks on Monday were his first public statements about the implications of Ms. Hochul’s 11th-hour decision since she announced it last Wednesday, saying she had directed the authority to “indefinitely pause” the congestion-pricing program out of concern that it would “create another obstacle to our economic recovery.”

The governor’s announcement created an immediate and substantial financial problem for the authority, which, for the first time in decades, was on the verge of having the money it needed to run and repair North America’s busiest transit system.

The program, the first of its kind in the United States, was to begin on June 30. Drivers entering Manhattan below 60th Street would have paid $15 during peak periods; trucks and buses would have paid more. Cities in Europe and Asia have adopted similar systems.

In addition to reducing traffic and potentially air pollution in Manhattan’s clogged core, a key goal of the program was to raise money to improve a mass transit system that is essential to New York City’s overall economic health.

Congestion-pricing-related revenue was earmarked for modernizing the signals that keep subway trains running, adding electric buses to the M.T.A.’s fleet and making more subway stations accessible for people with disabilities.

All those projects are in limbo after Ms. Hochul and state lawmakers ended this year’s legislative session last week without agreeing on a way to offset the $15 billion in revenue lost as a result of the governor’s decision.

Some people had speculated that Ms. Hochul’s move might prompt Mr. Lieber, who said the governor told him of her decision the night before announcing it, to quit. He said on Monday that doing so would be out of character for him.

He also countered suggestions that the authority’s board, which the governor controls, might proceed with congestion pricing on its own given that the program had been authorized by a state law. Approval from the state Department of Transportation would be necessary to move ahead, he said.

“The governor has been very upfront about the fact that that ain’t coming at this time from the State of New York,” Mr. Lieber said.

Although Mr. Hochul has not indicated when she thinks congestion pricing might be resurrected, Mr. Lieber said he and other authority officials remained optimistic that it would one day be in place.

“I’ll just say we at the M.T.A. are not giving up on congestion pricing,” he said.