VOICE OF David Brinkley: "Mr. President, can you please explain Reaganomics and what Reaganomics really means?"

Voice of Ronald Reagan: "Welll . . . certainly. Now I'd like to keep things simple so we can all understand. Let's suppose your mum baked a big blueberry pie. Now that pie represents the wealth of this country. Now take that pie and cut it in half. The top half is defense spending, the bottom half is for domestic programs and the other half is for the national deficit."

Brinkley: "Now wait a minute. We have three halves and a pie has only two halves."

Reagan: "No, you don't seem to understand. Let's look at it another way. You have three apples . . ." Excerpts from "The First Family Rides Again."

Rich Little is on the "Tonight Show," reading a letter from the First Fan.

"Dear Rich: "Welll . . . He draws it out in a voice that is so recognizable that the audience bursts into applause.

"You've done it again. I guess it should be some comfort to me that Nancy and I are able to provide you with so much material. It does concern me that you seem to be having so much trouble with the three halves of the pie.

"You are right on target about Americans and humor. We thank you for providing us with the opportunity to do one of the most important things anybody in politics should do--laugh at ourselves.

"With warmest regards, sincerely . . . Ron."

Little rolls The Name off his tongue and looks pointedly at Johnny Carson. Carson complains that he too does a lot of material about Ronald Reagan. "All I got was a letter saying 'Greetings.' " The audience howls.

Rich Little, who has more voices than some small towns have telephone listings, is hot right now because he does Reagan so well. "The First Family Rides Again," an album of tame, sophomoric Reagan spoofs, is Top 30, approaching 500,000 copies sold; K-Tel is about to start hawking it on television for Boardwalk Records.

The album was produced by Earle Doud, whose maiden effort, "The First Family," a 1962 spoof of the Kennedy clan, lays claim as the world's fastest selling album--close to 5 million copies.

Radio stations are playing several cuts from the new album--"Reaganomics," "The Big Game" (a poker battle between Reagan, Ford, Carter and Nixon), "Wake Up" and "Happy Birthday." The humor is decidedly soft: a press conference preceded by the opening theme for MGM Pictures; pokes at air traffic controllers, Hollywood, past presidents, midnight crisis calls, the president's age ("What would you like to be doing when you leave office?" Reagan: "Breathing.") "I have several rules of thumb," Doud admits. "I try and find something to talk about that everyone is familiar with. That's why there's practically nothing on the Reagan kids."

Rich Little adds that picking on the kids, particularly Ron Jr., could have been "a quick turnoff." "If you want to be a Mark Russell or a Mort Sahl, you're political and into making a point," says Little. "I'm not politically minded. I'm aware that if you're too tough on them the First Family , too cruel, number one you won't get play on the air and number two, you would offend the president." Little notes that, at election time, "I always vote for the guy with the best voice and encourage others to do the same."

Reagan: "Recurring dreams? You mean like I'm walking down a busy street without any clothes on, a gigantic naked woman with long, red matted hair comes crawling out of a dusty spider's web carrying long kosher salamis . . . is that what you mean Doctor?"

Doctor (excited): "Yes, what about those dreams."

Reagan: "I never have them."

As recently as the Carter administration, Doud says, "comedy albums were passe'. With this album, it's been a long time since there was anything like it. The Reagans have that Kennedy charisma and charm. And people buy albums about people they like. But it's important to be gentle. You don't particularly want to irritate the man in office, not that I'm a coward; but you wouldn't get the airplay if stations thought the president wouldn't like it."

Doud, who writes for Hollywood sitcoms "between administrations," is a veteran of the political-humor album. After "The First Family" (and a follow-up volume that sold only 300,000 copies), he also produced a string of less-successful records: "Welcome to the LBJ Ranch," "Lyndon Johnson's Lonely Hearts Club Band," "Spiro T. Agnew Is a Riot," "The Honest to Goodness We Really Mean It Very Last Richard Nixon Album," "Henry the First" (about Kissinger) and "Score Three Points." Ford "wasn't in office long enough and I couldn't get any record company interested in doing an album on Carter."

Word associations: "Summer?"

"Reagan: "These are tough. I'm thinking . . . Winter."

"Day?"

Reagan: "Night."

"Black?"

Reagan: "Welfare."

."Among those appearing on "The First Family Rides Again" is Vaughn Meader, whose meteoric rise as a comedian-impersonator ended with John Kennedy's assassination in Dallas. Meader was unknown before Doud heard him doing a quick Kennedy bit in a New York nightclub. After "The First Family" came out; he was suddenly a top attraction. Nobody could have guessed how that album would take off; only 40,000 copies were printed at first. When the demand became overwhelming, the record company "didn't have any jackets so they just put records out there without jackets," Doud recalls. "The pirates really had a field day because the records you can make in two minutes; it's the jackets that take a long time. We think another 5 million were pirated."

On "Rides Again," Meader appears for one line only. "He's a personality now," says Doud.

According to Doud, Meader became so associated with his Kennedy caricature that "it was very difficult for him to go on stage and do comedy after Kennedy's death because people thought they were looking at Kennedy, that it was bad taste. After a while, he fell to the wayside, didn't want to play small clubs, couldn't get it going."

Over the years, Meader has obscured his Kennedy looks with a graying beard and wide-brimmed Western hats, performed under fictitious names and stayed away from any Kennedy associations. Still the Kennedy identity lingers.

Right now, Little is promoting the album; there will probably be a follow-up and there's talk of a television special, as well. "I'm pleased with the result; nobody seems to be offended by it," he says. One cut that might have had that effect dealt with getting the president ready in the morning--putting his head on, then his arms, then saying "wait a minute, you forgot your brain," to which Reagan would reply, "Not again!" "A little thick humor there," Little says uncomfortably. "It was one cut that could have offended the president. We just took that off, a very good move."

Press conference: "Mr. President. Truman Capote from Bondage Weekly. What are you going to do about sadism in America?"

Reagan: "I think we'll leave that to the Democratic whips."

Voice: "Mr. President, we have the B1 bomber, the MX missile, the neutron bomb. What's next?"

Reagan: "Obscurity."

Just ask Vaughn Meader.