The time trails at Indianapolis Motor Speedway must appear very dull, with just one car drooning its lonely way four times around the 2.5-mile track. Today the solo runs will be completed and the 33-starters for the million-dollar, 500-mile race determined.

No matter what others feel, a half-million people paid $3 each to watch the trails last weekend.

"I just love them," says Donald Davidson, British-born but the U.S. Auto Club's authority on the 500. "They are neater than the race. One man and one car against the track the clock."

Today's action will become frantic as the 6 p.m. deadline nears. It is the car, not the driver, that qualifies for the race. If a car is bumped from the field by a faster entry, the driver is free to shop for another ride. They will run, not walk, up and down the line of waiting machines asking for a chance to steer one through the 10-mile test.

Last year Jan Opperman got under way just as the closing gun sounded. He completed the run less than two seconds quicker than rookie Eldon Rasmussen that bumped Rasmussen from the field.

The plan of putting the fastest qualifier on the pole (front row, inside lane) position began in 1915 when Howdy Wilcox burned the bricks for one lap at 98.9 miles per hour. In 1920 the system of 10-mile trails was instituted.

According to Davidson, the Speedway always has been open the entire month of May for practice. Time trials usually were held the three days before the race.

"You don't have to spend the whole month here," says Davidson, "but most teams find it helpful."

As Wally Dallenbach's STP crew did, for example. A brand-new car costing at least $100,000 had been built for him just for this race Dallenbach tried it out a few times early this month and found he wasn't comfortable in it. He's back in his year-old machine, and the new one is back on the trailer.

The month of May has two other virtues entrants aren't likely to give up easily: their commercial sponsors gain several weeks of valuable public exposure during practice and admission income from the two weekends of time trails help swell the purse to its present size.

The drawback is that very few top stock car drivers or European road racers care to give up that much time to one race. They would have to miss several races in their own specialty. Richard Petty could not afford an Indianapolis visit, as he frequently has said. It is not good business for him. Not one American stock car driver was among this year's entrants.

Of the road racers, Gianclaudio (Clay) Reggazzoni of Switzerland is out of action after suffering a practice accident and Belgian Teddy Pilette, grandson of 1913's fifth-place finisher, is a rookie with an under-financed team.

The solo run is more difficult than it appears. The track's four corners are not identical. Each must be entered differently to gain maximum speed. Winds are very tricky on the five-eights of a mile straightways. Only one rookie, Walt Faulkner in 1950, has ever won the pole position.

Starting position is most important. During the early stages of the race, traffic is heavy. The risk of running into a pileup is greater when starting from the rear of the field. Still Johnny Rutherford wound his way from 25th place to victory in 1974. He's starting 17th this year.

For all the excitement at the Speedway this weekend, the wildest race in Indiana in May has to be 40 miles north in Anderson. On the steeply banked quarter-mile teacup known as Sun Valley Speedway, the Little 500 was run last night.

For almost 30 years the Little 500 has matched 33 sprint cars, considered the most vicious and hard-to-handle racers of all, for 500 laps. The din is unbelieveable. The aroma of burning rubber and fuel seems strong enough to slice. The skill and bravery of the drivers is remarkable.

The bump and race their way around and around at about 80 miles an hour. The purse is $30,000. It's not Indianapolis, but a night like that in Anderson is usually enough for any racing fan.