JULIA CHILD is back. Her new 13-course weekly series, "Julia Child and More Company," has its debut tonight on WETA-TV (Channel 26, 9 p.m.). The first show is a menu for six persons featuring steamed mussels, rock cornish hens roasted with wine and a fresh fruit dessert. s

Last week she was here in person, charming an audience of WETA supporters during a lunch at the Capitol Hilton with an account of the path she followed from government file clerk to fillet cook. Washington played a significant part in her growth as a cook, she told her listeners. It was here, in an apartment on California Street during World War II, that she did her first cooking: "on a two-burner hot plate on top of a refrigerator."

Later, after her marriage to Paul Child, the couple bought a house in Georgetown and Julia tried to master the art of American cooking for two. "I'd consult a cookbook and start dinner at 6. We finally would eat about 10," she said with a laugh. Paul Child's assignment to the U.S. embassy in France led Julia to the Cordon Bleu, a friendship with Simone Beck and, after eight years of toil and testing, to the publication of Volume One of "Mastering the Art of French Cooking." Her book freed sauces and souffles from the selfish graps of Old World chefs and made them the property of anyone who could read and wanted to cook well.

Five publications later, in the book "Julia Child and More Company" (Random House, $15.95 hardcover, $9.95 paperback), Mrs. Child is still writing in English but with a strong French accent. The book, which presents the menus featured on the television series, includes such French classics as cassoulet, roast rack of lamb and a terrine of three fish. Over a private lunch at the Watergate (during which she had high praise for Chef Jean-Louis Palladin's oyster and sea-urchin soup, leeks and truffles in cream and a sorbet fashioned from passion fruit), she hastened to point to the offbeat and "new things" she will prepare. Among them are a vegetarian meal, a main course pie of rabbit and leeks, a butterflied loin of pork, monkfish and -- ironically -- a stewing chicken. "My market says there's not much demand for stewing chickens nowadays," she writes in the book, "because a lot of customers don't know how to cook them."

With her special blend of enthusiasm and determination, Julia Child intends to change all that and to convince viewers that entertaining with food can be as much fun for them as it is for her.

A number of other cooks who have fashioned books on their craft will be making appearances and doing cooking demonstrations at Bloomingdale's White Flint store this spring. Among the celebrities are: Joan Nathan ("The Jewish Holiday Kitchen") on March 21 and Pierre Franey ("The 60 Minute Gourmet") on March 27. Nathan will be at Bloomindale's Tyson's Corner store on March 20 and Craig Claiborne ("The New York Times Cookbook") will be at Tyson's only on May 28.

Dr. Geoffrey H. Bourne, the Australian medical educator who was the first to locate Vitamin C. in cells, was in town last week expounding on why there should be more nutrition education in medical schools. Not coincidently, students at the St. George's University School of Medicine, where Dr. Bourne is vice chancellor, have a compulsory, 48-lecture exposure to nutrition. (St. George's is located on the West Indian islands of Grenada and St. Vincent.The 650 students enrolled come from 23 countries, but the majority are Americans.)

"The American Medical Association recently said that the teaching of nutrition in medical schools is "inadequate," Dr. Bourne said. "They said much the same thing after a study they did 10 years ago, so I don't think we've seen much progress.

"Good nutrition is a fundamental part of preventive medicine," he said, "but a doctor can't really give you an answer when you ask him a question about diet and health. He's abrogated his responsibility and that opens the door for the lunatic fringe."

Dr. Bourne said St. George's medical training extends over 4 1/2 years, rather than four, "so we have been able to introduce nutrition without any strain." Students have responded well, he reported, and said that although "there are some faint stirringss of interest," among administrators, it may be student pressure that finally will force nutrition into medical school curriculums.

Dr. Bourne's concern is echoed in testimony given last fall before Sen. George McGovern (D-S.D.) at a Senate Nutrition Subcommittee hearing McGovern pointed out that only 30 of 129 medical schools require even 20 hours of nutrition. Nor has the government picked up the ball. "I am embarassed," McGovern said, "when my colleagues in the Congress allocate $60 billion a year for federal health care expenditures, but will not . . . earmark the insignificant sum of $1.5 million for seed money to develop nutrition education programs in our medical schools."