NEW YORK (CNN/Money) - The NCAA basketball tournament wasn't disrupted by the start of the the U.S.-Iraq war, but its viewership was.

After considering delaying the games, the National Collegiate Athletic Association decided last week to go ahead with the games starting Thursday, despite the start of the war the previous evening. But some of the games were shifted from their normal home on CBS to cable sports network ESPN. And even the games that appeared on CBS drew fewer viewers than a year ago.

CBS's decision to bump NCAA coverage to ESPN to make room for news coverage of the war cost it both viewers and ad dollars.

That shift cost the games some viewers and CBS, in the first year of an expensive new rights deal with the NCAA some as some games were shifted to cable to make room for news reports, and even the games that were broadcast on CBS had lower ratings than a year ago.

The average rating of the 17 games shown from Thursday through Sunday had a 4.1 rating, corresponding to the percentage of homes watching the game, according to an initial measure of viewership in the nation's 55 largest media markets by Nielsen Media Research. That's down about 19 percent from an average 5.8 rating for the 15 games shown in the first weekend a year ago.

Even excluding the four games that moved to ESPN, which is available in only about 86 percent of U.S. homes, the average rating for the weekend was about 4.9, off 16 percent from CBS coverage of a year ago.

The ESPN games got ratings between 1.2 and 2.0, compared with the comparable games that got 3.0 and 6.2 ratings a year ago on CBS. But all the games did worse than their comparable games in the year-earlier tournament, with declines of between 11 and 39 percent for the games carried on CBS.

CBS kept the television revenue from the national ad sales during the tournament games that moved to ESPN, although ESPN was able to hang onto the time set aside for local ad sales by affiliates, according to ESPN spokesman Mike Soltys. But CBS advertisers who saw the ratings for their commercials plunge below guaranteed levels likely will be due refunds or additional free commercials from CBS.

The NCAA was not the only big ratings event to have lower viewership due to the war coverage. The rating for ABC's Oscar broadcast Sunday evening was 25.3 in the 55 major markets, down from 29.1 a year ago, which put it on course to be the lowest-rated Oscars show in history.

CBS stuck with the NCAA tournament coverage Sunday even as ABC, which like ESPN is owned by Walt Disney Co. (DIS: Research, Estimates), bumped its own NBA coverage to ESPN to carry comments by President Bush and other war news.

ESPN had notified CBS that it would have trouble carrying NCAA games during Saturday and Sunday due to other commitments such as its own coverage of the NCAA women's tournament and the promise to make time available to ABC in case of news coverage concerns.

CBS officials were looking at using other cable networks owned by its corporate parent Viacom Inc. (VIA: Research, Estimates), such as MTV or TNN, or perhaps other cable networks, if ESPN had not been available when it decided to shift those games.

CBS games this coming weekend still could end up on ESPN again, Soltys said, depending on the demands of news coverage and ESPN's schedule. The games are set to resume at 7 p.m. ET Thursday.