You've probably heard about fast-talking Hollywood agent Norman Brokaw, whose latest client is the president's daughter, Patti Davis. But the other person behind Davis' suddenly promising acting and singing career is a slower talker -- Mississippi-born Larry Thompson, above. At age 36, Thompson is personal manager to Davis, as well as Cicley Tyson, Ernest Borgnine, Sally Kellerman and others. One of the ways Thompson will earn his 15 percent share of Davis' earnings this year is by making sure she isn't a flash in the pan.

"She's getting so much exposure because of her father," says Thompson. "You have to be very careful. You don't see Al Pacino or Jane Fonda doing the kind of press Patti does or being asked the kind of questions she's being asked. The interesting thing about Patti is really that her initials are P.D. and that stands for Patti Davis, not President's Daughter."

So far, of course, those initials haven't hurt a bit. NBC is paying Davis "an important six figures," as Thompson puts it, to appear in two television movies this year. For its megabucks, the network also may develop a series for Davis and she is forbidden to appear in features on other networks in 1981.

But Davis is free to pursue acting assignments in motion picture projects or, her other interest, music.Thompson hopes his client will release a country rock single this year or, possibly, an album.

"I'm sure everyone is thinking, well, this is just a president's child trying to capitalize on the spotlight," says Thompson. "But people are going to find her well prepared in the spotlight. She'll deliver."