By Peter Henderson

SAN FRANCISCO (Reuters) - Students appear to be carrying old PCs to school this year, computer and microchip makers say, confirming glum expectations in the technology industry and stoking fears holiday sales might also falter.

The back-to-school shopping season is a short and usually sweet period for personal computer vendors, and after more than a year of sluggish sales a boost is sorely needed.

Intel Corp.INTC.O , which makes microchips that power most PCs, said on Thursday that sales were trending toward the low end of normal seasonal trends.

Michael Capellas, president of Hewlett-Packard Co.HPQ.N , the No. 1 PC maker, has said repeatedly that the season began late and was light.

"Back to school was a little softer than we expected. Normally we see about a 50 percent rise in demand, but this year it was only about 35 percent," Capellas told investors on Thursday at a conference hosted by Salomon Smith Barney.

But Intel President and Chief Operating Officer Paul Otellini said retailers might be feeling the brunt of slow back-to-school sales compared with direct vendors, a group led by No. 2 PC seller Dell Computer Corp.DELL.O

"I think it is going to be less than people expected, but I don't think it's going to be as poor as looking only at retail (sales) would indicate," Otellini said in a conference call.

Dell said last month that consumer sales were strong. Gateway Inc. GTW.N , the No. 4 U.S. vendor which focuses on direct sales to consumers and has been losing market share, had forecast a "decent" back-to-school bump.

Consumers and businesses during the economic slowdown have shown little inclination to shell out for new computers that do not offer significant improvements, analysts say.

"After Windows 95 was released PCs have not changed so much," said Gartner Inc. analyst Mika Kitagawa.

Retailers have also spent heavily in back-to-school promotions and discounts, an expensive tactic which brought in some buyers in July, before sales faded, said Stephen Baker, who tracks retail sales on a weekly basis with NPD Techworld.

"We haven't been able to keep the ball rolling," he said. August sales would lag the previous year for desktops, while notebooks might be about steady, he said.

The roughly eight weeks of back-to-school sales count for about a fifth of annual PC sales, and they could also set the tone for the holidays, he said. "If you have a lousy back-to-school, you are depressed and it tends to dampen your expectations for Christmas."

National Semiconductor Corp.NSM.N , which makes chips for flat-panel computer displays, cell phones and other devices, said consumers might be depressed as well.

"The back-to-school impact seemed minimal at best," said Brian Halla, National's chairman and chief executive, on a conference call with analysts on Wednesday. "We are therefore hesitant to pin our hopes on a robust Christmas market."