Putin wants to take most of Ukraine, but a quick breakthrough is unlikely, the top U.S. intelligence official says.

President Vladimir V. Putin of Russia still aims to take most of Ukraine, but a breakthrough in the country’s east to other major cities beyond the Donbas remains unlikely in the short term even as Moscow’s forces consolidate their gains, the top American intelligence official said on Wednesday.

The consensus in American intelligence agencies is that the war in Ukraine is likely to go on for an extended period of time, Avril D. Haines, the director of national intelligence, said in her first public update on intelligence assessments of the war in more than a month.

Russia, she said, controls about 20 percent of Ukraine, with a conflict line that stretches for about 680 miles. Insurgent resistance by Ukrainians in Russian-occupied parts of the country is increasing, Ms. Haines said, making it less likely that Russia will make rapid gains or that a peaceful resolution can be reached.

Ukrainian forces have been able to hold many of their fighting positions in the eastern region of the Donbas, which includes the provinces of Luhansk and Donetsk. American intelligence agencies believe it will be difficult for the Russian military to capture the portion of Donetsk they do not already control.

Ms. Haines said the most likely scenario in the weeks and months to come was that “the conflict remains a grinding struggle in which the Russians make incremental gains, but no breakthrough.”

In that circumstance, Russia will have secured Luhansk, much of which it currently controls, as well as much of Donetsk and will have consolidated its control in southern Ukraine.

A less likely scenario is a breakthrough by Russia that would allow them to refocus attacks on Kharkiv in the northeast or Odesa in the southwest. Ukraine could also begin to stabilize its front lines in the Donbas and make some small gains.

“In short, the picture remains pretty grim,” Ms. Haines said.

Ms. Haines’ remarks came at a conference hosted by the U.S. Department of Commerce to discuss export controls. The Biden administration is trying to slow Russian weapon manufacturing by denying it components made with Western technology. Earlier in the day, Gina M. Raimondo, the commerce secretary, said that American and international controls had lowered exports to Russia of semiconductors and computer chips by 90 percent.

“It’s obviously left Russian companies without the chips and semiconductor they need,” Ms. Raimondo said.