No one who sells online has to be told how important the holiday shopping season is. For retailers, online or off, the fourth quarter is a crucial sales period. November and December alone can account for as much as 50% of a store’s annual revenues — and even more of its profits. And now it seems like every year the predictions of whether or not the holidays will be a good season come earlier.

This year high gas prices and signs of a slow back-to-school shopping season already have retailers and analysts nervous.

According to a survey of over 34,000 shoppers just released by the NPD Group, consumers are planning to start shopping later than they did last year and are hoping to spend no more than they did last year.

Last year 43% of back-to-school shoppers had already begun shopping by August 1st, and 51% shopped between August 1st and September 1st, but this year only 40% plan to shop that early, and 56% say they will shop between August 1st and September 1st.

They plan to shop later — but not shop more.

Respondents said they plan to spend approximately the same in 2006 as they did in 2005. In fact, 21% plan to spend less than they did last year.

On the positive side, 34% of consumers plan to spend more this year, and 43% expect to about the same.

Overall, almost half (47%) of consumers expect to spend under $250 a child this year, 28% plan to spend between $251 and $500 and 7% anticipate spending more than $1,000 for each child.

"Value was the primary decision criterion for what to buy and where to shop this year, and school requirements were also top of mind for many consumers," said Marshal Cohen of NPD, "but kids themselves still have a lot of power in the matter. Nearly a third of consumers said they would buy what their kids asked for."

While the NPD study concentrated on offline shopping, "The Voice of Women in America," a study from PersonalShopper.com based on a recent online survey conducted by MedeliaMonitor, found that more than half of all moms — fully 55% — are planning to do their back-to-school shopping online this year, and that is an increase of more 25% over 2005.

The reason for the jump? Moms see shopping online as the solution to their two biggest school shopping challenges: limited time and money.

When asked what their greatest frustrations were when shopping for back-to-school, 64% of mothers answered, "keeping myself and my children on the budget," and 42% said, "feeling stressed about getting it all done within the limited time have."

Although the US Census projects $6 billion will be spent on back-to-school shopping this year, many of the mothers in this survey made it clear that they plan to leave their cars parked at home and seek out family-friendly Internet shopping sites.

What does all this have to do with holiday shopping?

"In the last three years, back-to-school has been a clear indicator of what’s going to happen during the holidays," Mr. Cohen told CNNMoney.com.

Rising gasoline prices, while doing little to dampen summer travel, may finally be impacting the economy by weakening shopping. In addition, Mr. Cohen feels that the industry has not created must-have products, "Retailers and brands aren’t doing enough to excite consumers to shop for back-to-school. Unfortunately, I’m hearing the same rumblings about holiday 2006."

It is not the end of the retail world, holiday sales in the US are still predicted to grow as much as 3.5% this year, but that is not as vigorous as last year’s growth.

The big question for online retailers, though, is: Will an offline slowdown in holiday sales translate into an online speed up?

More here.