comScore examines the impact of a tightening economy and questions how much those tax rebates will help e-tailers.

The symptoms of a troubled economy are impossible to ignore: credit’s tight, housing prices are down and prices of consumer goods are up.

So what does all this mean for online retailers? According to comScore, e-commerce is feeling it more than the offline segment, and the main culprit is inflation.

“As you are obviously aware, the U.S. economy is facing some severe headwinds at the moment,” comScore Chairman Gian Fulgoni said during a conference call this morning. “e-commerce at this point is getting hit harder than retail sales in terms of growth rate. My hypothesis is that’s being driven by in inflation and the rise in prices for gas and food that have to be bought offline.”

With food costs rising and the price of gas marching toward $4 per gallon (the national average was $3.937 this week, according to the U.S. Department of Energy), Americans seem to be finding that they need to devote more of their monthly budget to these staples, leaving less disposable income for shopping online.

So far this year, online retail spending is growing at a much slower rate than previous years. Excluding auctions, cars and travel, e-ecommerce spending is up 11 percent so far in 2008, compared with 17 percent for the whole of 2007.

comScore reported that rising prices are the leading economic worry for consumers across all income segments, ranking well ahead of the issues of job security, rocky financial markets and falling real estate prices. Seventy-nine percent of comScore’s survey panel said they are cutting back on spending due to these concerns.

That is precisely what the Bush Administration’s economic stimulus program was supposed to address. But comScore’s research doesn’t project that the tax rebate checks will necessarily translate into the heightened consumer spending that retailers are hoping for.

About 70 percent of the people comScore polled said they would either use their check to pay down debt or put it in a savings account, an outcome very similar to what happened in 2001 with the previous tax rebate initiative.

“At this point, it doesn’t look like the economic stimulus package will have as much impact as the government would like,” Fulgoni said, though he admitted that what people say in surveys and what they end up doing are often different things. “I would imagine here that consumers will be spending more than they think.”

By segment, the high-end retailers appear to be the most impacted. Even though traffic to premium retail sites is still strong, spending is down, suggesting that those sellers are struggling with conversions or the average order size has decreased.

In contrast, discount and club retailers are faring better, indicating a more price-sensitive consumer.

The combined furniture, appliance and equipment category turned in the strongest first quarter among segments, followed by video games, which continued the momentum from the holiday season. The poorest-performing category was computers, with online sales down 17 percent from the first quarter of 2007.

comScore found more evidence of an increasingly price-conscious consumer base in its analysis of the sources of traffic for online retailers. An increasing portion of e-commerce traffic, and 51 percent of gross sales, comes through search.

For Magid Abraham, comScore’s CEO and president, that points to more consumers using the Web to research pricing.

“Search is becoming more and more the portal to e-commerce,” he said, adding that using the Web to comparison shop between retailers can also drives sales in the offline channel.

Nearly 80 percent of comScore’s panel said that the Web will become more a more important tool for researching prices than it is even today, the company said.

“Price sensitivity is on its way up,” Abraham added.

After search, comScore found that e-mail marketing delivers 8.7 percent of retailers’ visitors, but their purchases account for 14.2 percent of overall sales. Advertising provides 10.4 percent of all e-commerce traffic, but those referrals only translate to a slim 1.3 percent of total sales.

But search itself may be feeling the negative effects of the economic climate. After scanning the search engines, comScore concluded that the portion of search results that carry sponsored links is declining.

Looking only at Google (NASDAQ: GOOG), the decline is sharper.

A previous comScore report showing a steep drop in the total number of paid clicks on Google’s search pages set off a minor panic among investors, which comScore then sought to defuse by explaining that Google has been trying to improve the relevance and quality of its search ads by cutting out unrelated placements.

Nevertheless, the decline could be another symptom of a contracting economy.

“That may be a sign that advertisers are not spending as much money on paid search,” Abraham said. “It’s pretty clear that 2008 has started on a softer note than most e-tailers have expected.”