Automobile technology has moved further in the last five years than in the preceding 25. Throughout the 1950s and 1960s, the rate of innovation was held down by the enormous costs of introducing any significant change into a product that was the world's leading example of mass production.

But now the pace is being forced by the emissions controls the federal government requires and the fuel efficiency the customer demands. To stay in the market, the auto companies are having to adapt regardless of cost.

From the end of World War II into the early 1970s, there were only three major technical improvements in American cars. The automatic transmission became widespread in the early 1950s. Most models adopted the disc brake, at least on the front wheels, around 1970. The transition to a more reliable and durable electrical system began with the adoption of higher voltage in the mid-1950s and continued with alternating current over the next few years and electronic ignition by the early 1970s. It was a time of stable design in a stable market.

Then Congress passed the Clean Air Act in 1970, with its elaborate schedule of steadily tightening standards. In 1973, the first oil crisis arrived and, a few months later, the gasoline lines.

As engine technology stood five years ago, emissions and fuel consumption were trade-offs against each other. To cut one, the designer had to let the other go up. The challenge was to reduce both together, and the incentives, meanwhile, were repeatedly increased by the rises in the cost of gasoline.

In 1975, the catalytic converter appeared -- the crucial advance in pollution control. Now front-wheel drive is rapidly becoming standard for small cars. There have been continuous improvements in lightweight body design. New materials -- high-strength steel alloys and plastics -- are being introduced. Computer-controled carburetion is now going into production.

What comes next? Herewith a couple of vignettes from a brief visit to the General Motors Technical Center near Detroit.

GM was reluctant to put the computer under the hood because it's expensive, but it became necessary to meet the emissions rules. It's currently built into GM cars for the California market, and next year it will go into all GM cars.

Once the company decided to install it, the computer became an invitation and incitement to the engineers to see what else it could do for the car. It's a neat illustration of the way technology develops.

First, the computer can continuously adjust the idle setting, so that the engine idles when cold at the same speed as when it's warm. That saves gas.

Second, and more important, it can continuously adjust the timing of the engine to the octane level of the fuel. At present, a mechanic tunes your car to the fuel that's in it. If you go to a higher octane rating without changing the timing, you're wasting your money. If you go to a lower rating -- because it's cheaper or, as in last spring's shortage, because you can't get anything else -- your engine will knock hideously.

Knocking is explosion of the gasoline vapor in the cylinder instead of smooth burning. The designers can put a simple audio detector on the cylinder head to tell the computer when the knocking is getting serious. The computer then retards the spark, which takes care of the knock. If youu should then get a tankful of high-octane gasoline, the sensor will tell the computer that the danger of knocking has vanished, and the computer will advance the spark to increase efficiency. That raises miles per gallon.

This capacity for spark adjustment in turn gives the designers an invitation to increase the compression ratios of the engines -- even though they will be running on unleaded fuel, and high-octane unleaded fuel is not always easy to find. High compression further increases mileage. One thing leads to another.

Another example of the new technology: in the past, it was important to design cars that looked streamlined. Whether they actually were aerodynamically efficient made little difference in a time of cheap gas. But streamlining is often counterintuitive -- that is, the most efficient design doesn't necessarily look it.

Both GM and Ford engineers have recently been spending a lot of time in Lockheed's wind tunnel in Georgia. (Ford has also been testing its 1980 Lincolns and Marks in the University of Maryland's wind tunnel.) A GM engineer has on his desk a chart showing hours in the wind tunnel, by year. The line starts sharply up at the time of the 1973 oil crisis.

Now GM is building its own gigantic wind tunnel at its Technical Center. At 40 miles an hour, the typical car uses half its power to push its way through the air. Like everything else that affects gas mileage, streamlining has suddenly ceased to be a matter of cosmetics and is now being treated as an urgent matter for serious engineering research.

But consider the implications here: it will be GM that has the tunnel -- just as, for example, it was GM that first developed the catalytic converter. Technology is formidably expensive in a mature industry like automobiles. There are four American car companies, and one of them clearly has greater resources than the others.

What would you do about that if you were president -- of GM, or of the United States? The normal terms of American competition forbid these companies to collaborate. But without access to GM's emissions-control technology, for example, Chrysler would be out of business, regardless of the federal aid that Congress is extending.

Last spring Chrysler went to the Justice Department and asked for an exemption permitting it to deal with GM. The department granted it, and GM is selling its technology to Chrysler on the same terms that it sells the same technology to its own divisions. But Ford then went to court, protesting that the effect of the rule was to exclude it from technology that was being shared, in effect, by three-quarters of the industry. The judge agreed. The Justice Department is now appealing.

Some sort of pooling arrangement, probably with federal participation and support, seems to be in prospect. But since it is mainly GM's technology that is being pooled, it is technology developed mainly with GM's specific competitive requirements in mind.

Congress didn't intend it, in writing the Clean Air Act. Nobody foresaw it when the price of oil and gasoline first started to shoot up six years ago. But changing the rate of technological innovation in an industry, it turns out, inevitably changes the structure of the industry itself.