WE HAVE no secrets. What is required are time and patience, that's all."

You can at least believe the time and patience part when Jiae Knez, proprietor of Nonomura Studios at 3432 Connecticut Ave. Nw, sets a large china bowl on the workbench in front of you. She says it was brought to her in six pieces.

The six pieces you can't believe until son-in-law Hyon-Ju Sim (expert cabinetmaker as well as a china restorer, together with his wife, Pamela) points out hairline cracks in the rim that are visible only at an angle. The painted designs that cover the bowl have been retouched, but this is apparent only from the slightly rougher glaze. The new paint itself is indistinguishable from the old.

It turns out there is a secret to fixing china: It takes five or six years to learn to do it, according to Knez, who's been at it 19 years. Each job takes two to three weeks, depending on the severity of damage. What makes repairs especially difficult is that some owners try to fix a piece with the wrong materials, like epoxy-resin super-glues advertised on TV. The idea irks Knez into volubility.

"We see them come in with a piece they tried to fix in five minutes, and destroyed completely," she says. "We couldn't even take it . . .We try to save it as much as we can. We love the art and hate to see people go and destroy it."

A while back, you had to send damaged china to New York if you wanted good work done. "Maybe 10 or 20 years ago," says Mrs. Knez, "but no more. Now New York people send work to us."

Repairs are make with epoxies or the liquid porcelain used in dental work. The resulting bond is temperature, water-and stress-resistant enough so that a restored piece can reassume its old duties, whether in a showcase or on the dinner table. Just one caveat, says Pamela Sim, "We don't recommend that they be put in the dishwater."

Before you take a piece of china to a professional repair shop, it's sound sense to assess the item's worth, both real and sentimental. Restoration varies from $12-$18 for a chipped dish, to $30 and up for a smashed one. The above-mentioned bowl cost $45. DOING IT BY THE BOOK

There are enough self-help manuals on the market to belie craftsmen's claims that only a pro can do the job right. But to play it safe, test the books' advice (and your talents) on a cheap item. If you have none, buy an ordinary plate and fragment it with a light rap of a hammer.

Materials for most simple restoration jobs are cheap and available at hardware stores, arts and hobby shops. BOOKS

All About Repairing Pottery and Porcelain by David Everett. (New York: Hawthorn Books, 1976.) Covers everything from simple repairs to moulding and modeling, coloring and enamels. Includes list of manufacturers and mail order suppliers.

Reader's Digest Guide to Home Repair (New York: Reader's Digest Association, 1977.) Covers everything from broken porcelain to leaking faucets.