For the four-week period ended last night, ABC averaged a 4.1 rating and 11 share among adults 18-49, 0.3 rating points ahead of second-place CBS, according to projections provided by CBS. Last year the two networks tied for first during sweeps.

Final numbers will be out later today.

ABC’s average declined a mere 5 percent from last November’s 4.4 average despite losing “MNF,” a top-10 show last fall. “Dancing with the Stars,” which had the month’s two best showings among total viewers, helped make up for “MNF’s” loss.

NBC was third with a 3.7/10, up from 3.3/9 last year, and Fox fourth at 2.9/8, down from 3.2/9 last year.

But as strong as ABC appeared during sweeps, and as dominant as it’s been this season, winning nine out of the first 10 weeks of the season, it’s facing a lot of problems at midseason and is not assured its first No. 1 finish since 1999-2000.

For one thing, its midseason schedule, which it began rolling out two weeks ago, has been a disappointment. “Day Break,” the drama holding “Lost’s” 9 p.m. Wednesday slot until the latter returns in February, has averaged a mere 3.0 rating through two episodes, less than half of “Lost’s” average.

“Big Day” and “Help Me Help You,” its two new sitcoms, averaged an alarming 2.3 in their first night together Tuesday, pulling ABC’s nightly rating a full point behind its season average.

“Desperate Housewives” and “Lost,” while still powerhouses, have seen rating declines of more than 20 percent this year.

And unlike last year, when it finished 0.1 behind Fox among 18-49s for the season, ABC does not have the Super Bowl or Bowl Championship Series, which gave it big boosts in January and February.

Fox instead has the BCS, which should help it dig out of its immense fall hole along with returning “American Idol” and “24.”

Still, ABC did have the most impressive sweeps of any network, and not just among 18-49s. It came within 0.1 of tying CBS among adults 25-54, with a 4.7/12 to the latter’s 4.8/12. NBC, whose big gains are mostly due to “Sunday Night Football,” averaged a solid 4.3/11 and Fox was well behind at 3.1/7.

CBS led among households with an 8.2/13, followed by ABC at 7.4/12, NBC at 6.7/11, and Fox at 4.5/8.

Projections for the CW were not immediately available, though it’s expected to finish even to or slightly ahead of last year’s WB average and slightly behind UPN’s in its target demographic.

Through the first 25 days of sweeps, the network was even to the WB’s average in 18-34s with a 1.5. It may move up a bit, however, as it has had its best Monday and Tuesday performance of the season this week in the demos at a 1.6 and 2.0 rating, respectively.