Six weeks ago, Detroit's automakers appeared to be on course in their turnaround efforts despite a steep downturn in auto sales.

Ford Motor Co. surprised Wall Street with a $100 million first-quarter profit, and General Motors Corp. felt it had made the necessary cuts. Privately held Chrysler LLC said it was on track to meet its investors' goals.

But now, with gas at $4 a gallon and many consumers shunning fuel-thirsty pickups and SUVs, the Big Three are revising their strategies to cope with what appears to be a third oil shock, similar to the crises of the 1970s.

Ford is planning further cuts of up to 12 percent of its white-collar work force, and GM is expected to lay out further cost-saving measures next week at its shareholders' meeting.

Ford CEO Alan Mulally said it grew evident that the auto market was going through a fundamental transition, and the recent spike in gas prices above $3.50 marked a crucial tipping point. "It was clear to us that it was time to act," he told reporters last week.

While all automakers and parts suppliers are struggling in this climate -- even Toyota Motor Corp. has forecast a drop in annual earnings -- Detroit's automakers are most vulnerable to shifts away from vehicles that are traditionally their top sellers and top money-makers.

Three years ago, large pickups accounted for 15.2 percent of U.S. light vehicle sales, and compact cars accounted for 15.7 percent. Today, compact cars represent 20 percent of the total and the pickups' share of the market has slipped below 10 percent.

"Part of what they're dealing with is a cyclical downturn in the economy, and part of what they're dealing with is a lasting change in the kinds of vehicles that people want to buy," said Dana Johnson, chief economist at Comerica Bank.

Tight credit, falling home values and sagging consumer confidence also have dampened demand, but auto experts say it's gas prices that will have the most profound effect on the industry.

"The U.S. auto market appears to be headed to a rerun of the late 1970s, where the energy crisis, along with CAFE requirements, sparked a sharp shift to smaller cars," Lehman Brothers analyst Brian Johnson wrote in a report.

"There is a strange similarity today to what happened in 1973, and was repeated in 1980," said Gerald Meyers, former chairman of American Motors Corp. and now business professor at the University of Michigan. "I recall Jeep suddenly going dead in 1973. Dealers said overnight 'we have no traffic.'  "

The current rise in oil prices, above $120 a barrel, reflects strong demand from booming emerging economies such as China that is offsetting the drop in U.S. demand due to the economic slowdown. High fuel prices are sparking protests in Europe, where fuel is more heavily taxed than it is in the United States.

Most economists don't expect oil prices to subside as they have in the past, and a recent Goldman Sachs report evoked the prospect of a barrel of oil costing as much as $200.

Lehman's Johnson cut his share price targets for GM and Ford, saying he believed that a recession was priced into the automakers' weak stock prices, but not the structural shift.

Edmunds.com, an online automotive research site, described the shift as "bigger and faster" than any it has tracked. "This shift has precipitated dramatically over the last two months," it said in a study released Wednesday. "Until March, this pattern of segment migration had been accelerating markedly but rather gradually."

The Big Three are now slashing production of trucks and other large vehicles. Johnson estimates GM's output of full-size trucks and SUVs will be 40 percent lower this year, while Ford is expected to assemble nearly 30 percent fewer F-Series trucks.

Such production cuts are painful, but many in the industry say they're essential. In any case, Detroit's automakers also are under pressure from new mileage regulations to produce more fuel-efficient vehicles and technologies.

"It's a tough decision, but it needs to be made -- it's better to adjust now than later," said Joe Serra, a dealer whose stores include Al Serra Chevrolet-Buick-GMC in Grand Blanc.

"We're seeing a lull now, but I think it will bounce back this year. But when it does, people will be buying different types of models."

Most automakers had predicted a rebound in the second half of 2008, but some are less optimistic, though they still believe the second half will be better.

May appears to have been a slightly stronger month than April, when sales slumped to an annualized rate of 14.5 million cars and trucks, compared with last year's total of 16.1 million.

Investment firm Deutsche Bank is forecasting May sales around 15.2 million, at an annualized rate, and down 8 percent from year-earlier levels on a comparable basis.

Deutsche Bank analyst Rod Lache estimates car sales rose, but not enough to offset a 25 percent to 30 percent decline in light truck sales. He believes Detroit's automakers fared badly, with GM sales expected to fall 16 percent for a 21.9 percent share of the light vehicle market. Ford's sales are expected to be down 16 percent, Chrysler's down 12 percent, and Toyota's down 5.5 percent. The Japanese automaker has slowed output of its full-size Tundra truck built in Texas and Indiana.

"We believe the mix shift away from trucks continues to accelerate," Lache said.

The Big Three have relied in recent years on trucks for their earnings, generating well above $10,000 in profit on each pickup. "With pickup sales apparently falling below a 10 percent category share rate, large SUVs below 3 percent, and steel costs almost doubling, the profit pressures are rising above those of a typical recession," Johnson said.

Not only are Detroit's automakers selling fewer pickups and SUVs, but they are earning less on the trucks they sell. According to Edmunds' data, prices for large trucks and large and mid-size SUVs slipped, while small and mid-size car prices rose.

The production cuts are having a crushing effect on suppliers, especially small, privately held companies, said Jim Gillette, a supplier analyst at CSM Worldwide.

"It's just awful for many of them," he said. "I'm getting calls asking 'How will we make it through this?' "

In 2000, about 17 million light vehicles were built in North America. That number will drop to 13.65 million this year, he said.

The unexpected deterioration of the market appears to have wiped out most of the gains that Detroit's automakers achieved last year in the landmark contracts they negotiated last year with the United Auto Workers.

But David Cole, chairman of the Ann Arbor-based Center for Automotive Research, said that without those contracts, Detroit's automakers would have more difficulty competing in the growing car segments.

Currently, the Big Three do not even build subcompacts in U.S. plants. GM has them developed and made in South Korea, and Chrysler concluded a deal with Nissan Motor Co., which will supply the U.S. automaker with subcompacts starting in 2010.

The latest job-cutting announcements add to the economic difficulties in Michigan, which is one of the states, along with Florida and California, that has been most severely affected by the recession and housing crisis.

Tammie Weick, a worker at Axle & Manufacturing Holdings Inc., said the 12-week-long strike she recently endured convinced her to leave the industry and seek a career in nursing. She will begin school in September, while continuing to work for American Axle to provide health care for her five children, the youngest of whom is 2.

"It's very disappointing," she said about the walkout. "I'm ready to move on."

Economist Dana Johnson said he thinks Michigan's economy will recover more slowly than the rest of the country.

"I've always thought that 2009 would be another year of contraction for the Michigan economy. GM and Ford's announcement reinforce the view that that will be a difficult year," he said.