On any given night in the District, as many as three of the city's 10 general hospital emergency rooms normally will ask fire department ambulances not to bring any more patients because they have all they can handle.

But last Tuesday night, for the first time in memory, seven of the 10 emergency rooms closed their doors to ambulances for over two hours. Of the three remaining hospitals, only one, the Washington Hospital Center, was a major center with specialists on hand.

It's not that there has been an over-whelming number of emergencies, hospital officials say. Rather, the emergency rooms are full because the hospitals are full. There have been so few empty beds in city hospitals recently that patients have been stacked up in the emergency rooms waiting for beds to empty upstairs in the wards.

For years, health planning experts have been saying that the metropolitan Washington area has too many hospital beds. And hospital administrators say that the current shortage of beds does not change that long-term outlook.

But that's little comfort to hospital officials who have found, for reasons no one can fully explain, that their hospitals have been operating at virtually peak capacity for the last three to nine months.

"I don't know what's going on," said Dr. Dennis O'Leary, medical director of George Washington University Medical Center. "But I'll tell you, our occupancy has been going up, but that has not been as much stress and strain on us as the mix of patients -- they've been much sicker.

"It's not something we can put our finger on," said O'Leary, commenting on a situation which other hospital administrators say they, too, are experiencing. "But there are more patients with multiple problems, who don't come in with a nice, clean, single problem.

"I don't think there's an epidemic of anything in the community," he added, and I have a hunch that it's something we'll look back on in time and it will be an unexplained occurrence."

But in the meantime, he said Thursday afternoon, "I've got three beds (available) right now and one possible admission in the emergency room, and two of the beds are in the coronary care unit. We've had two, three and four patients in the (post-operation) recovery room on some mornings waiting for beds."

O'Leary said, "We really have been pushing as hard as we reasonably can to discharge patients who might not have been discharged quite as fast before. But our discharges are falling because what we've got left are really sick patients." He said the hospital was now putting off patients who can choose when they have surgery performed. "We've not had to do that for years and years," he added.

"We're probably 45 beds short of what we need right now," said Dr. Stanford Roman, medical director of D.C. General Hospital. Despite the fact that D.C. General recently gained 18 beds that were not available during a renovation program, the hospital is jammed.

"Most of the people coming in are very sick," said Roman. At first he thought it was people coming in after summer vacations to have surgery performed. "But now it's getting a little far beyond that point," he said. "Usually our peak period is January through March. I really can't explain this."

The increases in admissions and severity of illness are not confined to the city. Officials at Suburban Hospital in Bethesda, and Fairfax, Commonwealth Doctors and Mt. Vernon hospitals of Fairfax County, report that they are experiencing the same phenomenon.

"We have a severe bed shortage," said a Suburban spokeswoman." We're at about a 96 percent occupancy rate and we are probably seeing a sicker class of patient."

At Fairfax Hospital, spokeswoman Peggy Pond said, "We're seeing more complicated illness, but nothing specific." Fairfax usually fills about 82 to 85 percent of its beds, said Pond, and is now filling about 92 percent.

While the figures may seem to indicate that the hospitals still have empty beds they can use, they are usually staffed for occupancy rates around 80 to 85 percent. When these rates hit 95 percent, the hospitals are, in effect, filled to the bursting point.

There are, in fact, about 1,000 empty hospital beds in the area, with about 400 in the city, 300 in Maryland and 300 in Virginia.

The 1,000 beds are those that the hospitals are licensed to use but have not because of not enough staff or not enough demand or because of renovation programs, such as D.C. General's.

Barry Wilson, vice-president for Blue Cross/Blue Shield here, sees the current crunch as an aberration in the otherwise downward trend in local hospital use.

The number of days patients spent in District hospitals declined about 6 percent between 1970 and 1978, Wilson said, but during that time there were short periods when occupancy increased. The question, he said, is whether the current trend will continue.