Motorists frustrated by shortage of unleaded gasoline and its high price have destroyed as much as $1 billion worth of anti-pollution equipment in their cars by using regular leaded gasoline instead of unleaded, according to federal officials.

Increasing numbers of motorists appear to be resorting to such "fuel switching," and the U.S. Environmental Protection Agency worries that the trend will intensify as gas shortages continue this summer.

Officials say the trend could undermine efforts to clean the nation's air.

When lines of cars waiting to get gasoline began to lengthen in Washington in recent weeks, reporters saw motorists pumping regular gas into cars requiring unleaded. Station operators say many motorists here are doing this.

One Washington area motorist was seen using a child's toy horn as a funnel at the pumps so he could put regular into his car's smaller unleaded gas intake, which is designed to thwart just such action.

Officials say that burning as little as two tanks of leaded gas in a car designed to take unleaded will wreck the delicate catalytic converter - a $150 to $300 item that is the key to the antipollution system in most late-model American cars.

There are about 40 million cars on the road with a total of $7 billion in catalytic converters, the EPA says. Detroit started producing cars with the converters in 1975 in response to federal clean-air rules.

The EPA estimates on the basis of surveys that 10 to 15 percent of the owners of these 40 million cars are fuel switchers. One EPA survey suggested that the proportion may be even higher in California, an EPA spokesman said.

Unleaded gasoline is in somewhat shorter supply than regular and premium leaded because federal price controls and other rules have tended to discourage refiners from producing enough, officials and industry representatives say.

The problem is bound to intensify as Detroit turns out more cars designed for unleaded gas each year, they say. In 1975 unleaded accounted for only about 13 percent of total gasoline consumption. This year it will account for more than 40 percent, with demand soaring for unleaded while demand for regular gradually drops.

"Once people are out of gas they'll use anything rather than not drive," said Benjamin Jackson, an enforcement official for EPA. "'We believe that's what is happening in California."

While service station operators can be fined $10,000 for pumping leaded gasoline into a car requiring unleaded or for allowing anyone to do so at their pumps, there is no penalty for an individual driver who does so.

However, the EPA is presurring the states to inspect for auto emission levels in regular state inspection programs and expects that all states will do this by 1981. When this happens, motorists who have switched fuels may be forced to shell out $150 to $300 for a new anti-pollution equipment.

Virginia now looks at anti-pollution equipment during semi-annual automobile inspection to insure that the devices have not been removed. No local jurisdiction now inspects, however, to insure that the equipment is working properly to control emissions.

Nobody is exactly certain how far the supplies of unleaded fall short of demand, and how much switching the shortfall may be causing.

The EPA's Jackson thinks the shortfall may be very small - even tiny - but quirks in the gasoline distribution system and other factors may make it seem pronounced in certain areas of the country.

American Automobile Association surveys of the Washington area's 1,500 service stations show that at any given time more are out of unleaded.

Last Wednesday, for example 6 percent of the stations contacted were out of unleaded, while only 3 percent were out of regular and 1 percent out of premium.

A week earlier, 19 percent had been out of unleaded, versus only 5 percent out or regular and 3 percent out of premium.

"Continually, unleaded seems to be the one running out most, and it's going to get more so as the percentage of new cars on the road increases, said local AAA spokesman Glenn Lashley.

Random interviews last week with late-model car owners in Prince George's and Montgomery County shopping center parking lots disclosed no admitted fuel switchers, although several people said they knew others who had switched. Some also said they knew of people who were hiring mechanics to remove their catalytic converters or had done so themselves.

Switching because of an increasing inability to find unleaded gasoline at service stations now seems to be assuming significance in addition to two other reasons causing people to switch in the past - the higher price of unleaded fuel and its lower octane.

Unleaded is more expensive to produce because additional equipment is needed to produce it and it must be handled with special care so it won't be contaminated with lead in the distribution system.

But that only accounts for a penny or two a gallon, according to EPA. Oil companies and dealer pricing practices - particularly making leaded regular a "loss leader" to attract customers - have made unleaded even more expensive than regular.

In Washington, full-serve unleaded this week cost an average of 87.7 cents a gallon, or 3.9 cents more than the average for regular, according to the AAA.

The EPA has agreed with the U.S. Department of Energy to keep the price difference between regular and unleaded to less than 5 cents according to DOE's price control system in order to discourage switching.

Drivers also switch to regular because it often has a higher octane rating than unleaded. Octane is a measure of a gasoline's ability to resist "knocking" - a pinging noise heard if fuel ignites too soon in a car's cylinders.

Lead prevents knocking and has traditionally been used for this purpose as an additive to gasoline. But lead also pollutes.

Unleaded gasoline is given resistance to knocking by additional processing and by other additives than lead. But because this is so difficult and expensive, unleaded tends to have lower octane levels than many new cars need. The Independent Gasoline Marketers Council says new cars need 92 octane gas while most unleaded currently is only 87 octane.