Peter Jennings (search) hasn't returned to the air since his April 5 announcement that he has lung cancer, but he's often shaping "World News Tonight" from behind the scenes.

Jennings sometimes participates in the 9 a.m. daily conference call to set assignments for the day, said Jon Banner, executive producer of "World News Tonight" (search). Banner will fax scripts to Jennings, who will frequently call or e-mail suggestions.

"He clearly can't be involved to the extent that he was when he was on the air every day, but we are lucky that he is involved to the extent that he can be because there's no one better," Banner said Wednesday.

Besides being anchorman, Jennings is listed as the broadcast's senior editor, and he's fulfilling that second role "on the days that he's able to," Banner said.

He would not discuss Jennings' condition.

Jennings, the longest-running anchor on one of the three network evening newscasts, last delivered the news on April 1. In a husky voice, he taped a message to viewers that was aired April 5 detailing his diagnosis.

Charles Gibson (search) and Elizabeth Vargas (search) have subbed for Jennings. Gibson and Bob Woodruff handled the bulk of the anchor duties for the coverage of Pope John Paul II's death and Pope Benedict XVI's selection.

Jennings had said that he hoped to continue anchoring when his treatment permitted, but there's no indication when that will be.

"We have told him that whenever he wants to come in, we're ready for him," Banner said.

"World News Tonight" had slowly narrowed the gap with NBC's market-leading "Nightly News" before Jennings' announcement, and the ratings have been little affected by the change. Last week, "Nightly News" averaged 8.6 million viewers to 8.5 million for "World News Tonight."

ABC hasn't begun to count the cards and letters that have come in wishing Jennings well.

"The response of the viewers has meant a lot to him," Banner said. "The response has been enormous."