Comcast’s chief executive, Brian L. Roberts, did not even mention the network on Comcast’s earnings call with investors last week. Instead he raved about the health of the NBC Universal cable channels, which drive the profitability of the division. Those cable assets increased revenues by 12 percent, to $2.1 billion.

Robert Seidman, the co-editor of TV by the Numbers, a ratings Web site, said Comcast “knew what it was buying and knew what it was getting with the broadcast network.”

But the network Comcast bought had several pillars outside of prime time — the “Today” show, “The Tonight Show” and “Nightly News” — that had weathered the storm. Lately, there have been concerns inside the network that even those stalwarts might finally be subject to fallout from prime time’s underperformance. One senior news executive, who asked not to be identified commenting on the entertainment division, said, “Prime time is painful.”

But for the moment at least, those concerns are more about shrinking leads over competitors than shrinking audiences. “Today,” which hasn’t lost a week in the ratings in almost 16 years, has maintained its audience (even adding to it slightly) this season, though the No. 2 show, ABC’s “Good Morning America” had added more viewers and closed what was once a yawning gap to just a sizable one. ABC has also inched closer in the evening news ratings, though NBC has added viewers to that top-rated program as well.

In late night, which traditionally has a closer relationship to prime-time ratings, some impact is noticeable. “The Tonight Show” with Jay Leno, which enjoyed more than 15 years of dominance over CBS’s “Late Show With David Letterman” (not counting the period of upheaval when Conan O’Brien replaced Mr. Leno), has fallen behind CBS four weeks out of the first six this season in those 18-49 ratings — the first time that has happened since 1994.

Of course, Mr. Leno was infamously exiled for a time to the 10 p.m. hour where his show was pummeled — particularly by NBC’s own affiliates — for low ratings. But this year two new NBC 10 p.m. shows have fared even worse. The Monday drama “The Playboy Club” was an instant flop. A new entry on Thursday, “Prime Suspect,” has been more highly regarded and is still on the air, but last week averaged a puny 1.2 rating (about 1.5 million viewers in the 18-49 group).

NBC’s new leadership made clear internally that the rebuilding process would take time and that extreme patience would be required. One senior NBC executive, who asked not be identified discussing the network’s internal strategy, said, without disclosing specific figures, that the budget for developing new shows was significantly increased last spring, to the same levels as the other networks, after years of cutbacks. (NBC’s previous owner, General Electric, had pared budgets in preparation for selling the company.)