It's not just the heat, it's the humidity. Or maybe it's the pollution. Or maybe it's a combination of all three, but whatever it is that has made the past week so miserable will be back within 24 hours.

The seven day air pollution alert with its air quality index as high as 140 - over 100 is "very unhealthy" - ended at 2 p.m. yesterday as warm humid air flowed in off the Atlantic dumping its humidity in the form of showers, cleansing the air and keeping the temparature at a comparatively bearable 85.

U.S. Weather Service forecasters say another flow of hot, humid air from the southwest should reach here today or Wednesday, the same kind of air that swamped the area last week with temperatures up to 100 and humidity up to 85 per cent.

While the seven-day pollution alert caused a lot of runny eyes, runny noses, sore throats and accompanying foul tempers, there is no direct evidence it caused any deaths.

In fact, there is little direct evidence that it even caused, or causes, any short-term serious illness, according to some research done by Dr. William Howard, chief allergist at Children's Hospital National Medical Center.

"Three or four years ago I worked with a nice young lady down where they do all the pollution counts and got 18 months worth of admissions to Children's and D. C. General (Hospitals) and got the particulate matter (pollution) counts and we could't fit anything together in terms of admissions," said Howard.

"The thing that bothers us the most is the humidity tied in with the air pollution," said Howard. Last week when the "humidity began to rise and it got clammy, then it all worked badly and everything went to pieces," particularly for the asthma patients.

"When the humidity is high the kids are more uncomfortable," said Howard. "It's harder to breathe. The heat and the humidity are both very bothersome. Obviously the pollution adds to it, but it's a two-way street."

Howard said that asthma admissions to Children's have been running two to four a day in the past few weeks, double the one to two such admissions a day the hospital usually sees. Both he and other allergists stressed that only a very small percentage of patients are being truly sickened by the weather.

"Surprisingly there hasn't been that much of an aggravation of symptoms in most persons," said Dr. Robert Scanlon, who has a private pediatric practice in Montgomery County and is codirector of Georgetown University Hospital's allergy clinic.

"We really haven't had a marked increase in the problem load over the past week or two," said Scanlon. "We do have individual patients who feel that when they go out their conditions are aggrevated by the pollution."

"A lot of people who go from the suburbs to the city seem to have irritation of the eyes and the nose and some feel they do more coughing. But with our clinic patients (at Georgetown), people who live in the inner city (and go to the clinic), we haven't seen a marked worsening of their condition."

Both Scanlon and Howard emphasized that one reason for the apparent lack of problems is that those who are most susceptible to the environmental condition may be heading the repeated warnings and staying indoors.

Whatever is causing asthmatics to have trouble breathing is getting worse, believes Howard. "We used to have seven to 10 admissions (of asthmatics) for the month in July. Now we're running 40 to 50 for the month.

"I have a suspicion that what we're seeing is a whole change in the environment," he said. "When I came to this hospital as chief resident in 1937, we had an occasional asthma admission, but nothing like this.

"When I was in practice here I used to see kids with asthma and I'd treat them and they'd go home and do fine. But it's just gotten worse and worse," said Howard. "I think the combination of air pollution and humidity make the difference," he said, adding that he is sure the pollution is a factor in the problem "but I can't make the computer prove it."

Philip Witorsch, chairman of pulmonary medicine and director of the intensive care unit at the Washington Hospital Center, said "we expected that we'd seeing a lot more pulmonary patients. But I think people have been aware of the air pollution indices and have been staying indoors.

"There's no really good data on what happens to healthy people in this humid, polluted weather," he said, "but healthy people notice more discomfort," especially if they insist on jogging, playing tennis, or engage in other strenous activities that cause them to gulp down deep breaths of filthy, humid air.