Don't think you were the only American who didn't quite grasp everything President Carter had to tell you about his energy plan Wednesday night. Neither did his mother.

"I didn't exactly understand," she said yesterday with typical "Miss Lillian" candor at a Peace Corps potluck lunch, "but I thought he looked good."

It brought down the house and set the pattern for what was to follow in the 78-year-old ex-Peace Corps volunteer's hour-long exchange with reporters and other ex-Peace Corps volunteers.

Seated in a vintage Peace Corps headquarters' chair (reportedly sat in by all Peace Corps India desk officers, whose ranks she joined in an honorary capacity), to no one's surprise at all she had comments and answers - some irreverent, of course - on a broad range of subjects. For instance:

She thinks energy is "nice" and she believes in what her son is doing "for you all," but as for herself she isn't what she calls "an energy freak";

She thinks the President was pleased with his reception on the Hill but later Wednesday night when she saw him (barefoot and in blue jeans) back at the White House she didn't ask him;

She did not call United Nations Ambassador Andrew Young "a windbag";

She did not say she was a prisoner in the White House only that she was a prisoner in Plains;

She had "no comment" on Indira Gandhi's defeat and told the President of the United States so when he called her after the election;

She never once got "delhi-belly" when she was a Peace Corps volunteer in India;

Sampling home made cuisine of Swedish, Thai, Indian and other international origins, the President's mother reminisced about her two-year Peace Corps stint in a health clinic northeast of Bombay. "don't get me talking about India, honey," she warned one youthful "alumna" seated on the floor at her feet.

She "loved" India, it never did get too hot for her. In summer, her feet blistered, in winter they "rotted." She lost 19 or 20 pounds, alternated wearing two dresses all the time she was there, cut her own hair, ate fruits you could peel and never had any protein.

This year, when she returned as her son's personal representative to the funeral of Indian President Fukhruddin Ali Ahmed, "I didn't see a single poor person" in the village where she used to live. "I think Mrs. Gandhi got things ready."

While Indira Gandhi's political fate was a subject she avoided ("she was so charming to me, that's one thing I never discuss"), she was loquacious about others.

Like the time this winter when "Jimmy called me at the Pond house" at Plains and said the temperature was 65 degrees at the White House and what did she have her thermostat set at?

"About 85," she said she told him.

Then there was the Andy Young incident. Just the other day she mistakenly told a White House telephone operator ("they screen all the calls, you know") she didn't know him when told "Ambassador Young wanted to speak to her."

Of course, she'd known him - for 20 years - but as Andy and "I didn't call him that (windbag) - oh, no." The way it happened, she said, was during an interview with ABC's AM Amercia host David Hartman.

Somehow, something got taken out of context about the time she said "Andy Young talks a lot - I've known him for 20 years - and he's the only one I listen to." That part, she said was "cut off".

She wrote him a little note later. "He was coming to see me anyway." They're getting together at 3 p.m. today because she is going home to Plains on Saturday.

"I got a dog in obedience school thereand his time's up. He knows more than I do, anyay."