RATINGS for “The CBS Evening News with Dan Rather” have slipped to alarmingly low levels.

Rather’s newscast – which claimed a few first-place victories in early 1998 and last summer – is now ranked far behind NBC’s “Nightly News,” anchored by Tom Brokaw, and ABC’s “World News Tonight” with Peter Jennings.

Rather’s viewership slid 12 percent in the second quarter of this year compared to last year – while averaging nearly 1.6 million fewer viewers than Brokaw and 1.5 million fewer viewers than Jennings. By comparison, Brokaw’s “Nightly News” experienced a 1 percent bump in total viewers, while “World News Tonight” grew by 6 percent.

To date this season, “Evening News” is down 4 percent in households, compared to the “NBC Nightly News” (down 8 percent) – while “World News Tonight” remains unchanged.

Still, over the last two years, “Evening News” has lost only 5 percent of its viewership.

Some insiders believe that Rather – who’s been with CBS more than 40 years – might be stretching himself too thin.

In addition to his “Evening News” anchor duties, Rather also hosts “48 Hours” and is a contributor to “60 Minutes II.”

The veteran newsman – who inherited the “Evening News” reins from Walter Cronkite in 1981 – is also a tireless, globetrotting field reporter who’s usually in the thick of the action.

Others, like “Evening News” executive producer Al Ortiz, point to CBS’ troubles in rebounding from viewer boredom over wall-to-wall coverage of the Monica Lewinsky scandal.

“ABC came back from that and we never did. We’re not entirely sure why,” Ortiz recently told the Associated Press.

Ortiz also told the AP that CBS’ lack of a strong morning show – like NBC’s “Today” show – might be contributing to Rather’s low ratings.

“If there’s a big story going on … and you start your day with another network, it’s tough to draw people over to us at 6:30 in the evening,” Ortiz said.

Rather was out of town yesterday and unavailable for comment.