President Reagan used his influence so that Dennis Wilson, the late Beach Boys drummer, could be buried at sea by the Coast Guard, the President's spokesman confirmed today.

Mr. Wilson, 39 years old, drowned Wednesday while diving off Marina Del Rey, Calif.

Federal rules prohibit burial at sea except for veterans, and Mr. Wilson was not one. Scattering of ashes is permitted.

Larry Speakes, the White House spokesman, said Mr. Wilson's family took Mr. Reagan up on a promise he made this summer when the Beach Boys visited the White House. The President said then that he would be glad to help the Beach Boys if they ever needed it.

The offer followed an apology by Interior Secretary James G. Watt for barring the Beach Boys from performing in Washington at the Fourth of July celebration.