Riders of Washington's Metro subway overwhelmingly prefer it to anything else and more than one-third of them say they would be either riding in a car or a cab to make the trip if the subway were not available, according to a Washington Post survey.

Most subway riders say they think the cost of the trip is reasonable, but are less than enthusiastic about dealing with Metro's farecard machines or the complexities of transferring between the bus and the subway.

The Washington Post survey of subway riders was conducted last Tuesday, with 2000 passengers returning brief questionnaires handed out at random at 12 selected subway stations between 7 a.m. and 2 p.m.

Because of the difficulties of follow rigid polling procedures under the crush of a morning rush hour, it would be misleading to state with conviction that the survey's findings are "correct" within any specified narrow margin of error.

Despite that limitation, those interviewed are believed to be close to a representative sample of subway users. The survey, therefore, should provide a fairly accurate look at passengers served by the 17-mile network and their attitudes on a typical day.

The survey shows that in the far-flung inner urban ring including the Washington downtown area. Rosslyn and Crystal City Metro is taking large numbers of people out of cars.

Metro's popularity with its riders is underscored by the fact that four out of five of them said they preferred the subway to the kind of transportation they would have been using if there were no subway. That percentage was about the same for both those who said they would be taking the bus instead and those who said they would be riding in a car instead.

One-fourth of those surveyed said they would be using a private car and another 11 percent said they would be in a taxi in response to the question: "If there were no Metro subway what one means of transportation would you most likely be using now?" Almost all the rest said they would be on a bus.

Of the rush-hour regulars who answered the question, 22 percent said they would use a private car and 2 percent said they would use a taxi, Rush-hour regulars were those who told The Post they use the subway boarded the train between 7 and 9:30 a.m.

Of all the others interviewed, almost half - 48 percent - said they would have used a car or a taxi for the trip if there were no subway.

Assuming the average downtown auto occupancy of 1.5 persons per car, and disregarding all the taxi riders on the assumption the taxis would be cruising anyway, the survey results could mean that 12,000 fewer car trips were made Tuesday between 7 a.m. and 2 p.m. than would have been made if there were no subway.

There has also been some evidence that Metro is hurting the downtown taxi business, a Diamond Cab spokesman told The Washington Post recently, although definitive numbers are not available.

The survey results do not mean that Metro has solved the traffic problem. The 12,000-car total is less than 4 per cent of the 323,246 vehicles that entered the downtown Washington ring (including Rosslyn and Crystal City) between 7 a.m. and 2 p.m. during a traffic count conducted in April 1975 by the Metropolitan Washington Council of Governments.

Edwin Haefele, a University of Pennsylvania political science professor who specializes in transportation economics and is familiar with Metro, said he would make two points:

Reduction in auto congestion "probably will not occur" without restraints on auto use because it has been the experience of road planners that "if better roads are less congested, they are automatically filled up."

"I don't know who feels that Washington would not be well served by a downtown distribution system" such as Metro. Haefele said, but he added that it would be an error to assume that gains transit makes from cars on downtown lines could be "transposed to those long lines" Metro plans to extend to the suburbs.

Metro planners obviously disagree with that observation. The first major suburband line to Silver Spring, opens Feb. 6, but most planners think Metro will not have a real test on auto-reduction capability until it reaches the Beltway. That is scheduled to happen next November with the opening of the New Carrollton line.

Metro general manager Theodore C. Lutz said that although he was surprised by the high number of Metro riders who said they would have been in cars instead, he was not surprised to find people in that category. "One of the things that has interested me," he said, "is the degree to which people will ride the train but not the bus."

Almost three out of five of those surveyed Tuesday (the survey did not include the evening rush hour) got to the subway stations by means other than the bus. Thirty-eight percent walked and another 15 per cent drove.

Since all stations were not included in the survey, those statistics could vary depending on the nature of the stations not surveyed. However, an attempt was made in selecting the stations to reflect the system as a whole.

Lutz was pleased with the findings that 65 per cent of those responding rated the courtesy of Metro employes as either excellent or good.

"That number would undoubtedly have been lower a few months ago," Lutz said. "When the trains were not running well, there were inevitably more confrontations between station attendants and equipment repairmen with the public than there are now, and those people were under incredible pressure. We've also made some changes there."

Three out of five of the Metro riders in the survey gave the cost of the ride a favorable rating, but 10 per cent thought it was too much. Two-thirds thought the subway's speed was favorable, but 12 percent did not: 57 percent thought Metro was reliable, but 13 percent did not.

Reliability has improved dramatically since last July and August when the Blue Line opened, but there was a major breakdown during the Monday morning rush hour, the day before the survey was taken. More than 97 percent of Metro's train have been completing their schedules in recent weeks.

The farecard machines, which vend and read the magnetically encoded tickets Metro riders must use both to enter and leave the subway, drew a mixed review. A total of 35 percent gave the machines a favorable rating, but 36 percent were unfavorable.

The complex procedure of transferring between bus and train was rated unfavorably by 31 percent of the riders, but favorably by 29 percent. Those perceptions can be expected to very widely from person to person depending on where they transfer. At the Pentagon, the transfer is fairly convenient, with bus bays right on top of the station. At Potomac Avenue, it is ridiculous, because in the evening people have to troop across Pennsylvania Avenue and stand in a field for their buses.

More than half of Metro's riders are employed by either federal or local government or the military - not a surprising statistic considering the city the system serves.

Those surveyed are also, for the most part, young and fairly comfortable financially. Almost half of those responding were under 30 years of age and 84 percent were 44 or younger. Three out of five were in families where the total income was more than $18,000 a year, and three out 10 come from families with total income of more than $30,000.

Three-fourths of the riders were white and 21 percent were black. The rest were of Oriental or other descent.

Metro carries a lot of commuters, but if has an unusually high ridership during midday when compared with other systems. Almost two-thirds of those surveyed said they were going to work, but another one-fourth said they were taking job related or personal business trips.

Questionnaires were handed out at Rhode Island Avenue, Union Station, Metro Center, Farragut North, Dupont Circle, Stadium-Armory, Potomac Avenue, Capitol South, L'Enfant Plaza, Rosslyn, the Pentagon and National Airport. Boxes to collect the questionnaires were placed in all Metro stations near all the exits.