White House medical experts strike a cautiously optimistic tone.

Vice President Mike Pence and his team of medical experts struck a cautiously optimistic tone on Monday night, saying California and Washington had seen “remarkable progress” for slowing the spread of the virus by following guidelines to stay at home and avoid congregating in groups.

And they expressed hope that social distancing efforts were beginning to work.

“That’s a great tribute to the people of both of those states, and to all of their dedicated health care workers,” Mr. Pence said. “We’re beginning to see a leveling.”

“It only becomes a trend if every one of us continues to take ownership,” Mr. Pence added.

Dr. Deborah Birx, who is leading the administration’s coronavirus response efforts, cautioned that the most recent data on the virus’ spread was not as accurate as experts would like it to be. She said at least one county in the New York area had seen a significant surge in cases over the weekend, and that officials were concerned with cases rising throughout Louisiana, Illinois and the Washington, D.C., area.

But Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, joined the optimistic tone. Dr. Fauci, who has been rooted in explaining the virus through a scientific lens — especially when the president is talking — said that the number of hospital admissions and intubations in New York had seemed to level off.

“So we just got to realize this is an indication, despite all the suffering and the death that has occurred,” Dr. Fauci said, “that what we have been doing has been working.”

He added that he still would be reluctant to declare premature victory over a virus whose spread has been unpredictable.

A point of contention between Dr. Fauci and Mr. Trump has been the president’s willingness to reopen the country despite overwhelming scientific evidence that the country is not yet in the clear.