It took all of 30 seconds from the time Nick Kniska said goodbye to Jimmy Carter for the 16-year-old Lanham resident to become a celebrity.

Beseiged by calls from the media, Kniska was interviewed, photographed, filmed, taped and congratulated by friends on into the early evening, an unsetting experience for someone whose name has never been exactly a household word.

Despite astouding odds, another Lanham resident who lives just about 5 blocks from Kniska also get through to the presidential talk show yesterday. But for Leslie Tfenniger, 21, 8703 Good Luck Rd., there was comparatively little media fuss, perharps because her call was one of the last while Kniska's was one of the first. And Kniska's question, to say the least, was bold.

"Mr. President . . . I would like to know why your son Chip and your daughter-in-law and your grandson are living in the White House on taxpayer's money . . . not in their own house earning a living." He then followed it up with a question challenging the right of the President's daughter-in-law to use Bethesda Naval Hospital for her recent childbirth.

Nick said he was "satified" with the President's answers (that he and his family paid their own ways and were not "mooching off the American taxpayers.) "But I guess there's no way of checking it." he said.

"I was excited when I was talking to him," the De Matha High School sophomore said.

"I thought they would cut him off," said Nick's best friend, John Piccirilli, who was serving as Nick's press secretary at the home yesterday, answering calls from reporters and taking messages.

Nick said he had always wondered why President Carter would allow his son, daughter-in-law and grandson to live in the White House at taxpayers" expense.

"We've from a military family. Any they're always accusing the military for having so many benefits at taxpayers' expenses.

So yesterday around 1 p.m. Nick dialed the President's number. He said the first two times he got a busy signal but on the third time someone answered.

Nick's parents said they were proud of their son for asking the questions. "I give him a lot of credit for taking the initiative to get his questions answered from the horse's mouth," his father, Nicholas E. Kniska SR. said.

"I'm just so flabberglasted," Mrs Kniska said since he talked to the President."You'd think he was Secretary of State," said his father. As they talked, Nick shouted. "Here I am." and turned up a local radio station where they were playing a tape of his voice.

"When you want an answer, you call somebody who can give you the answer." said Tfenniger, explaining why she called President Carter.

A May, 1976 graduate of Elizabethtown (Pa.) College, she said she asked the President if the restrictions on appointments to civil service positions could be lifted. Lifting the current restrictions, she said would improve her chances of gaining a job for as a statistician. She said she's applied for a position directly to the Civil Service as well as to several federal agencies.

"He said he'd look into my case and I'd receive a reply this week." Tfenniger said. "I'm very satisfied with his answer. I believe he'll do all he can.

Tfenniger said she's been unemployed since her graduatio. She attended school year-round to able to graduate in three years. She has bachelor's degrees in both psychology and sociology.

"I didn't expect to get through," she said, "but I knew I was going to try."

The satistics courses required for her degrees fulfill Civil Service requirements for a statistician's position, she said.

Tfrenniger said she began dialing the White House at 2 p.m. She said the telephone there began ringing at about 2:20 p.m. and she stayed on the line for a half-four until a person answered, told her her call would be accepted, and said she would be called back to talk to the President.

Tfenniger talked with the President for about four minutes, she said. She said she was nervous, but "I don't think my nervousness showed too much."