The crowd of about 650,000 people had gathered through the day for the Fourth of July concerts and fireworks display on the Mall. Unfortunately but predictably, they all wanted to leave at once, some 250,000 of them on the subway. It was the largest single day of subway ridership that Metro had ever seen.

Crowds flocked to the Smithsonian station and could hardly get near the escalator, much less down onto the platform. Once there, the air was sweltering; 10 or more people fainted and had to be carried away. You could get to the platform at Capitol South, but it took some doing to board jammed subway cars. Some people walked to other stations, only to find escalators and platforms packed and trains overflowing.

Metro officials say they anticipated throngs. Some 354 subway cars -- every one that could run -- passed through the stations every four to six minutes until 2 a.m. Although it was not in evidence at every station, Metro employees at the platforms were using "flow control": they radioed other employees at the escalators to stop letting people in. This worked at some stations, but transfer points were another story.

No one was shoved onto the tracks, and no one was trampled. The crowds seem to have been generally good natured. That the number of people who passed out from the heat in the subway stations was minuscule in relation to the over- all ridership led Metro officials to say they han- dled the situation well. But there may have been a certain amount of good luck involved. As many as 1,000 people were being packed onto six-car trains, and in such hot and irritating conditions it is not hard to imagine some scenarios of pure terror.

Metro wants 600 cars in operation by the time the full system is completed. At least as many will be needed when the system is called upon to move, quickly, the tens of thousands of people who assemble for special events such as the Fourth of July. Even then it will be necessary to be ready with crowd control procedures considerably more effective than those used on Thursday night. The visible presence of extra Metro personnel is a key factor. It was a traffic nightmare for many people to get home. It could have been a real nightmare.