It isn't surprising that the White House didn't answer the letter from Brian Spangler and the Cub Scouts of Den 3, Pack 229, in Oakland, Calif. It was a pretty angry letter.

But then, the Cubs were pretty angry.

Last spring, the boys had collected cans and glass bottles for recycling, had worked on a solar energy project and even had taken their parents through their homes looking for ways to conserve energy.

For this they expected to receive the President's Energy Conservation Award for Cub Scouts, as promised in a pamphlet from scout headquarters.

Instead, they were informed that the program had been canceled.

On June 20, Brian and his den wrote to President Reagan to protest. "We are very mad . . . Because of what you did, we think people won't really really care about conserving. And they will waste energy.

"You're canceling smart stuff, good ideas. Why were you elected president??? Because you said you'd cut taxes. But this is not a good way to cut expenses.

"Please write back to explain why you did this." Brian and six friends signed the letter.

Brian was in school yesterday, and couldn't be reached, but his mother, Katie Spangler, said Brian and the other boys composed the letter at a den meeting in June. "We had to tone it down some," she said.

There was no response until last week, when a letter to Brian arrived: "Dear Mr. Spangler," it began.

"Although this program has ended, we want to commend you and the other members of Den 3 . . . for your conservation efforts. Wise and efficient use of our energy resources in this country is a key element of our national response to the world energy situation."

It was signed, "J. Michael Power, director, Policy, Planning and Evaluation, Conservation and Renewable Energy, Department of Energy."

No offense, said Mrs. Spangler, but to Brian it wasn't the same as a presidential certificate.

An Energy Department spokesman said yesterday that the certificate program was part of the Carter administration's response to the gasoline lines two years ago.

Citations were widely distributed in 1979 and 1980, but the program expired some time between Reagan's November victory and the early months of the Reagan administration, said Power. "I suspect it was one of the adjustments that occurred with the new administration," said Power, a veteran Energy Department official who said he didn't enjoy dashing cold water on the scouts' hopes.

"We have been curtailing all our outreach programs," Power said yesterday.

Another DOE official thought the program died quietly in the final months of the Carter administration. "Most of those people are gone now," he said.

In any case, no one told the scouts in Oakland.