As gas prices rise, consumers are bypassing the pump — and that potentially could throw a monkey wrench into auto sales expectations for the rest of the year. After gas sales rose in January and February, they have fallen each week since the beginning of March.

At an average price of $3.50 a gallon last month, 70% of national chains reported a drop in sales, according to MasterCard SpendingPulse. “Compared to March 2010, we’re seeing drivers pump less gasoline,” said Michael McNamara, vice president, MasterCard SpendingPulse.

“Based on what we’ve observed in the last three to four years, high gasoline prices typically result in consumers consolidating shopping trips, shopping closer to home, and making fewer trips to the brick and mortar locations as we get to Saturday,” he said.

Historically, a sharp increase in fuel prices has been followed by a decline in demand for SUVs and other large vehicles. There also has been a corresponding increase in demand for compact cars and electric or hybrid vehicles.

In a perfect world, that would be great news for new sales of hybrid and electric vehicles. But the continuing challenges in Japan have had a disproportional impact on hybrid and electric vehicle production, as well as the availability of key parts such as batteries. So the vehicles that seem tailor-made for pricier fuel are those most likely to be in short supply — and consequently more expensive.

“The impact to vehicle production from the earthquake in Japan will limit the supply of many fuel-efficient cars like the Toyota Prius,” said Jonathan Banks, executive automotive analyst for the NADA Used Car guide. “These vehicles were already tight on inventory and over the next month demand should easily outstrip supply in the new market, driving more consumer demand towards used cars and trucks.”

Many analysts cite U.S. job growth as the main reason they remain bullish that new car sales will end up even higher than estimated this year. They believe now that more people are back at work, pent-up demand for new vehicles may push more consumers to the showrooms.

But those estimates downplay the impact of lost vehicle and auto parts production in Japan, which has suffered two more major earthquakes in the past four days. Shares of Ford (NYSE:F) and General Motors (NYSE:GM) were up slightly on Tuesday after falling about 3% on Monday Toyota (NYSE:TM) was up 1%.

In a related event, the Bank of Japan highlighted the auto sector as an area of particular weakness on Monday when it downgraded its economic forecast. The central bank attributed most of the challenges to damaged production facilities, supply chain disruptions and curbs on electricity use.

As of this writing, Susan J. Aluise did not hold a position in any of the stocks mentioned here.