The National Park Service is about to launch a study of a critical housing and overpopulation problem on some prime national parkland.

The focus of its research: the squirrels in Lafayette Park.

A biologist who has studied the squirrels estimates that 100 of them have taken up residence in the 8.5-acre park--and has advised the park service that that's too many. So out of concern that the critters might decide to move across the street to the White House -- where the presidential plants must be protected -- the park service wants to find out what attraction the park holds for the squirrels.

To do that, the Interior Department is recruiting people who are willing to volunteer two hours a week to help count the squirrels, observe what kind of food they eat and photograph their activities. Among the things the park service wants to find out is whether the squirrels are eating vegetation -- or Big Macs left over from lunchtime picnics.

"We've got the largest population of squirrels ever recorded in Lafayette Park and they've never been studied," said Jenness Hall, who is in charge of the project.

Those interested in volunteering, should phone Hall Tuesday through Saturday at 755-7798.