When Cho Lin, wife of the vice premier of the People's Republic of China, entered the State Deparrment lobby yesterday afternoon for a formal luncheon, she applauded with the employes gathered to greet the Chinese dignitaries.

Her applause, accompanied by a warm, demure smile, was a sign of appreciation for the respectful crowd but also appeared to be an indication of her enjoyment of the politicial ritual of whirlwind public appearances.

"We have the feeling, as expressed in an old Chinese saying that 'we be come old acquaintances at first sight,'" Cho commented at one point yesterday.

And, in fact, in her first full day in Washington, Cho cheerfully broke out of the routines of protocol whenever possible. At Children's Hopital National Medical Cneter, she touched and kissed as mamy of the children as she could.

At 62, Cho is not a shadow of her husband but a forceful adviser on military affairs. For the last two years she has worked in the Chinese Communist Party's military affairs commission, and is reported to have the pivotal role of monitoring complaints at the party offices in Peking. She is a small woman of ample build, and wore gray slacks, sensible gray and beige shoes and a knot sweater under her brocade jacket. Her round face has small, delicate features and though her ears were pierced she wore no earrings.

Near the end of the luncheon givem by Grace Vance yesterday, Vice Premier Teng Hsiao-ping and Secretary of State Cyrus Vance entered the room and proposed individual toasts. Cho looked intently at her husband, smiling slightly. "It was a respectful, warm glance. She looked at him like Nancy Reagan used to look at Ronald during his speeches. Complete, interested attention," said Helen Dudman of the Public Broadcasting System corporate offices here.

In her own remarks, Cho Spoke Admiringly of the American feminist spirit. "American women are making a growing impact on change and progress in American Society. We have much to learn From you." Sen. Claiborne Pell(Dr. i/.), who was at her table remarked, "I thought it was well said. During the meal we had the normal lunchtime conversation, about my trip to China, about normalization of relations. She's bright and intelligent."

Her sensitivity also won over Rep. Margaret Heckler (R-Mass.), another luncheon guest. "She sounded very familiar with what she said. She wasn't forced, or awkward," said Rep. Heckler. "What amused me was that after she spoke of the women's movement, she used the Chinese words, to end her toast, that means 'bottoms up.'"

Immediately after the Whilte House arrival ceremony yesterday mornig, Cho made a 20-minute stop at the National Archives. Her tour of Chilfren's Hospital was twice as long In her limousine, she told on Satate Department official that she was particularly interested in the hospital because one of her three grandchilren had been born very small and was in an inculbator for three months.

While she was standing in the intensive-care nursery, a 1-day-old body had a breathing Iull. Cho's party was moved to another part of the nursery while the infant was treated. After a tense 10-minute waiting period, she walked over to the crib and checked on the infant, who was by the doing well.

In the toddler playroom, Cho spoke with Viola Cheng, a physician who grew up in Canton Province. Cho was born in Yunnan Province, according to the State Department biography, attended school in Peking and has been married since 1940.

As she left the hospital, she gave the chief administrator a blue procelain plate with a white crane and smiled. "I've seen a let of things," she said, "I think we can learn from you."