It's a familiar scene at the White House: The president, his hand cupped over an ear, shaking his head and saying he can't hear the questions reporters are shouting at him.

That may be a scene from the past, if a new "high-tech" hearing aid that the president began wearing last week lives up to its advance billing.

The device, which fits within the ear canal and is virtually invisible, contains an electronic circuit to help filter out the crowd noises that often prevent individuals with hearing loss from discerning conversations in a crowded room.

It probably won't make it easier for Reagan to hear reporters over the whir of a helicopter, but it should help improve his hearing in most "normal" conditions, said Thomas Powers, an audiologist with the manufacturer, Siemens Hearing Instruments Inc. of Piscataway, N.J.

The president suffers from a 30 percent hearing loss in his right ear, which he has blamed on an incident in his days as a movie actor when a 38-caliber pistol with a blank was fired close to that ear. He will wear one hearing aid in each ear for balance, a common practice and one the president adopted in 1985, shortly after he first began wearing a hearing aid. About 20 million Americans suffer a similar degree of hearing loss.

His new hearing aids, which cost about $1,900, contain a number of innovations not available on other commercial brands, according to the manufacturer.

"It's smaller, fits entirely in the ear canal," said Howard Girsky, a spokesman for Siemens, which announced the delivery of the aids to the president. "In the industry, the trick is to miniaturize and this is state of the art."

In addition to tuning out many background noises, the hearing aids contain a credit-card-size remote control device that also will allow Reagan to adjust the volume. They also have a special circuit designed to reduce the feedback roar that many people who wear hearing aids get when they use a telephone, Powers said.

Dr. John House, a Los Angeles physician who is the president's ear specialist, suggested the president be fitted with the new aids, which have been on the market less than a year. The president agreed, and he was fitted for the devices in December.

They were delivered last Tuesday, and Powers said they were an instant success. "It worked very well. He was happy with it and very pleased with the comestics," Powers said.

White House spokesmen said that the new devices were not acquired because of any change in the president's hearing and that the White House will be billed for them.