NEW YORK – His emergence as the last of the three evening newscast anchors from the ’80s is less than a month old. Now a battle against serious illness will put Peter Jennings’s steady, day-to-day presence in doubt.

His future suddenly seemed uncertain with his announcement yesterday that he has lung cancer. Mr. Jennings, who received the diagnosis a day earlier, plans to continue on ABC’s “World News Tonight” – as much as he can – after beginning chemotherapy next week.

Elizabeth Vargas filled in on “World News Tonight” yesterday, but Mr. Jennings taped a message to viewers about his illness.

“I will continue to do the broadcast,” he said. “On good days, my voice will not always be like this. Certainly, it’s been a long time. And I hope it goes without saying that a journalist who doesn’t value – deeply – the audience’s loyalty should be in another line of work.”

A former smoker who quit 20 years ago but resumed smoking briefly after the September 11, 2001 terrorist attacks, the 66-year-old anchor was too ill to work Saturday during the network’s special report on Pope John Paul II’s death. He hasn’t been feeling well the past few months and didn’t travel under doctor’s orders after December’s tsunami because of what was described then as an upper respiratory infection. He did go to Iraq in January for the elections.

Mr. Jennings said he was surprised at how fast the news traveled and at the kindness he had received from so many people. “Finally,” he said, “I wonder if other men and women ask their doctors right away: ‘Okay, doc, when does the hair go?'”

Lung cancer is the leading cancer killer in America, and roughly four out of five people diagnosed with the disease die within five years, said Dr. Cliff Connery, chief of thoracic surgery at St. Luke’s-Roosevelt Hospital in Manhattan. Mr. Jennings could be an inspiration for many Americans going through a similar fight, Dr. David Johnson, chief of oncology and hematology at the Vanderbilt University School of Medicine, said.