Agreeably warm air, rife with hints of spring, continued to sweep over midwinter Washington yesterday, luring strollers out in shirt sleeves and prompting unanimous consent among schoolchildren that it was a perfect day to be home.

As a matter of fact, that's exactly where 230,000 pupils in the Baltimore area were, thanks to the planning of energy-conscious school officials.

Both Baltimore City and Baltimore County decided to close thier schools as part of a midwinter energy-conservation plan adopted a year ago. so yesterday, as temperatures climbed itno the low 60s, students from 343 schools in the two systems were wondering whether to bundle up in shorts or light sweaters to get through what somewhat chagrined school officials a year ago judged would be the "worst week of the winter."

"I'm sure everybody would have felt more comfortable if it had been colder," sighed Albert Naeny, with the perspective only an assistant superintendent could have after Mother Nature again had outmaneuvered him. "Gut who would have thought the third week in February would have produced temperatures this warm?"

Naeny refused to rule out the possiblity of a cold spell that would make the school calendar seem like a brilliant piece of administrative foresight. "We still have three school days left . . ." he said.

Alas, for the not-so-prescient planners, the national Weather Service predicts the mild air and temperatures 15 degrees above normal will last through the week and into the weekend. The high today was 64 at National Airport at 2 p.m., 18 degrees above normal. Harold Hess. "When it's all done it'll probably be the warmest week of the winter, at least since the first of the year."

But more than a year ago, when Baltimore County Board of Education President Rodger Hayden and his eight colleagues decided to substitute a week of vacation at Easter with a week off in midwinter, it was snowing hard, Hayden recalls. The board hoped to lower its $7 million fuel bill by $100,000; school researchers consulted the weather service and reported that weather during the third week in February habitually ranked as the winter's worst. The vote was 9 to 0.

"A lot of people are raising questions, but when you do this you have to look forward and history told us the week was pretty stinky, as far as weather was concerned," Hayden said. And he had found a silver lining: "The fact that the schools are closed and the weather is warm means we'll be saving even more fuel."

"Last year we had ice, the year before we had 22 inches of snow," said Baltimote City school spokesman Anne Emery. "We planned in good faith. We don't control the weather."

According to the National Weather Service, January on the averages is a colder month, but Baltimore school officials also considered snowfall and transportation problems caused by icy roads in pinning the Worst Week label on Feb. 16-20.

In county schools, Energy Conservation Week, as the vacation is called, reflects an increased awareness over the last four years of energy resources. Temperatures now are set at 65 in county schools, and the heat is turned off half an hour before closing in the elementary schools. Schools are heated only one night a week, when the PTAs meet, and the superintendent has been known to bring out shawls when school boards sessions stretch into the frigid evening hours.

"I don't know if everybody's thrilled to have a week off in February but there's been a good spirit about it," said Naeny.

Board president Hayden said travel agents were gleefully booking trips to Florida and Disneyland.

Despite the unseasonably mild weather, Baltimore County officials already have adopted a calendar for next year that includes another Energy Conservation Week at the end of February, and Baltimore City school officials are planning another Energy Saving Week for the city's 130,000 students.