The big US television networks began to unveil their Northern Hemisphere autumn programme line-ups yesterday in the first round of the scramble to attract advertisers, amid projections that they could be facing the toughest ad market for eight years.

Last year, the big networks - NBC, CBS, Disney's ABC, and Fox, owned by Rupert Murdoch's News Corporation - brought in US$9.6 billion from pre-selling slots in their autumn and winter commercial breaks, but forecasters believe the recession could crimp that number by up to 15 per cent this year.

That would mean the companies will rely even more heavily on the so-called "scatter market" of last-minute ad sales, which could make them particularly vulnerable if there is not an economic recovery in the US later this year. In turn, that could put dramatic downward pressure on the budgets for new programmes in future years.

"There are three or four sectors that are vital as advertisers for the television industry," said Vincent Letang, who heads a team of advertising analysts at the market researcher Screen Digest.

"Among those, one is the car industry, and automotive money is going away from TV. There is a direct chain of consequences from the recession, through poor consumer confidence to the worst auto sales in many years, which is hitting ad spending. What car companies can spend is being concentrated on advertising that directly promotes sales rather than in broad, nationwide branding."

Investment and banking firms are also cutting back on advertising, as are drug companies, fearful of a regulatory clampdown that could limit marketing claims for blockbuster drugs.

Meanwhile, advertisers continue to be wary of the declining market share of the networks, as they compete for viewers against cable rivals and the internet. Overall, Screen Digest predicts that advertising income for US networks could be down 13 per cent.

Some broadcasters are already experimenting with new ways to win audiences and to save money, cutting expensive dramas in favour of reality series and talk shows. Jay Leno, the late-night comedian, will be moving to prime-time for NBC, for example, and Fox has made a new season of So You Think You Can Dance, a talent contest, the centrepiece of its autumn line-up.

Fox TV - home to The Simpsons, 24, House with Hugh Laurie, and the most-watched show in the US, American Idol - was first to present its new season yesterday at a ceremony in New York for advertisers.

Observers described the line-up as particularly cautious.

The network has suffered the biggest decline in viewership this year and it is attempting to shore up its position with younger viewers more tempted by internet viewing of shows.

Fox is putting particular store in a High School Musical-style series called Glee and is also rolling out four new comedies, including a spin-off from the cult cartoon Family Guy.

The low-rated science-fiction series Dollhouse was surprisingly brought back.

A much-publicised move by Fox to sell fewer but more expensive commercials in its major dramas in 2008-09 has also been shelved. "We are going to use it strategically," said Jon Nesvig, Fox's president of sales.

"As much as I think it was a terrific experiment, week after week it was tough economically to make it work."

Screen Digest's Letang said it could be hard to interpret the headline number for upfront ad sales, which the networks could inflate by offering "non-monetary incentives", such as lower cancellation penalties.