In an emotional welcome to nine American families singled out for recognition by the White House yesterday, Nancy Reagan launched a newly instituted annual ceremony called the Great American Family Awards Program. At one point, when she mentioned her own family, her voiced cracked and she seemed on the verge of tears.

"My own family is the most important aspect of my life. Regardless of age, I'm still my parents' daughter and the family is very central . . ." she said, her voice trailing off. A sympathetic East Room audience of 200, including 55 members of the nine families being honored, came to her rescue with resounding applause.

Trying again, Mrs. Reagan managed to complete the sentence with ". . . to my life," then went on to tell her guests of a quotation she always liked. " 'The person who understands the meaning of life plants trees under which he knows full well he will not sit.' You are here planting trees."

The ceremony was the high point of a 10-month project launched last November in conjunction with President Reagan's proclamation of National Family Week. Organized by the White House Office of Public Liaison, under the aegis of the 7-year-old American Family Society (AFS), it called for nine families to be singled out of 200 selected by chapters of seven national organizations around the country.

Mary Elizabeth Quint, deputy special assistant to President Reagan for public liaison, said she enlisted the help of the AFS and its president, K. Wayne Scott, because "we needed someone who could coordinate on the outside, with Mrs. Reagan serving only as honorary chairman.

"Mrs. Reagan did not want it to be used politically. She and the president were very insistent that nothing should be used that had a political overtone," according to Quint, who had stressed both strong family units and free enterprise when she was president of the General Federation of Women's Clubs in 1978-80.

Working through the AFS, Quint said she and K. Wayne Scott lined up a panel of judges to make the final selection of the nine families. It included NBC "Today" show weatherman Willard Scott; entertainers Marilyn McCoo, Billy Davis Jr., and Marie Osmond; National Geographic Society vice president Robert L. Breeden and the Junior Miss for 1982, Susan Lea Hammett.

Quint and K. Wayne Scott also lined up Reader's Digest, Procter & Gamble, Atlantic Richfield, Kiplinger Foundation Inc., and Holiday Inns, among others, as corporate sponsors to pick up travel expenses for the winning families.

"The White House had no expense whatsoever," said Quint.

All the preparations and the close coordination with the White House resulted in a public relations success yesterday. "Our biggest turnout in a long time," said Sheila Tate, press secretary to Nancy Reagan. "All the local television stations want to cover their local families."

Willard Scott started it off on yesterday's "Today" show when he interviewed the Larry McCord family of Slapout, Ala. Asking them how Slapout got its name, McCord, a farmer, told him they had a general store there and when you went in to ask for something, the response was "I'm slap out of it."

The other eight families included a military family recently returned from West Germany and others from Alaska, Wisconsin, Hawaii, Iowa, Oregon, New York and Minnesota.

They were not "relics" of another time but were chosen, said Mrs. Reagan, because they represent what the American family can be in a complex and modern world: families headed by single parents, families with foster or adopted children.

"Someone once said that there are only two bequests we can give our families, one of them is roots, the other is wings. Families can help to provide both the security of roots and the inspiration of wings," said Mrs. Reagan. "And that's what these families have done."