A natural fiber whose best known use until recently was wrapping mummies now is being knit into fashionable sweaters and soon may even be woven into the fabric of America's textile quotas.

In the past two years, shelves of department stores, designer boutiques and haberdasheries have sagged under millions of garments made of ramie -- a hairy-looking fiber that also is known as China grass.

Imports of ramie garments -- mostly sweaters of ramie blended with cotton -- have tripled in the past year, because clothing made of ramie blends is not covered by quotas on imports of cotton fabrics.

The Reagan administration will try to mend that loophole this week by imposing quotas on ramie imports.

Ramie-blend sweaters account for nearly 10 percent of the sweaters sold in the United States last year, according to the Department of Commerce. Nearly 93.2 million ramie-blend sweaters were imported last year -- a 330 percent increase from 1984's 21.2 million sweaters.

"A market disruption has been created by the explosion of ramie imports in the apparel trade," said Donald R. Foote, director of the International Agreements and Monitoring Division at the Commerce Department. "It has caused severe economic problems for the textile industry in this country. . . . If it's disruptive, it should be included" in the replacement for the four-year-old quota agreement that expires July 31.

"One way of avoiding quotas was to come up with blends that would escape the limits," noted Babette Ballinger, president of Babette & Partners, a Manhattan sweater manufacturer. By mixing yarns not subject to quotas -- such as ramie, linen and silk -- with cotton, and making these nonquota yarns a majority of the fiber in a garment, importers could escape the quota restrictions.

But to some designers and retailers, ramie is a poor substitute for cotton or linen. "It doesn't have the feel of cotton, nor does it breathe as well or dye as well," Ballinger said.

Importers and retailers of ramie-blend garments, on the other hand, say they have found a new natural fiber that should not be restricted. Ramie "adds a new dimension to sweaters," said Jack Shamash, president of S. Shamash & Sons, the nation's largest importer of ramie fabrics. Shamash said ramie fiber is not produced in the United States. He argued that imports should not be limited because there is no domestic ramie industry to protect.

The source of the latest textile controversy is a hairy plant that is in the same family as flax, which yields linen.

Ramie has been cultivated for thousands of years -- often for making rope. It only started appearing in apparel here about two years ago, shortly after the United States tightened quotas on cotton imports.

Ramie was the favored choice as a cotton-quota beater because of its cost: about $1.35 a pound compared to between $2.70 and $3.25 for a pound of linen, Shamash said. Although ramie costs about twice as much as cotton, it might be cheaper to import in the end because it is not subject to quotas, which add about $20 to the price of a dozen sweaters, Shamash said. Additionally, the duty on ramie goods is about 10 percent less than duties imposed on cotton merchandise. A ramie-blend sweater "sometimes costs a lot more than a cotton sweater; sometimes, it costs a lot less," Shamash said.

As the largest importer of ramie, Shamash is bullish on its properties. He said it adds to a sweater a special silky luster that is missing from a pure cotton item.

Others are less enthusiastic. In Washington, Britches of Georgetowne has decided not to sell ramie blends in its men's clothing stores and carries a small amount of ramie in the Great Outdoors stores, which offer more informal clothing. "It doesn't stack as well next to cotton," said Clair Murik , a buyer for the Great Outdoors stores. "Cotton has more spring and takes brighter colors; ramie is more flat, tactile and nubby" -- a look that isn't appropriate for Britches, she said.

"If I had my druthers, I'd use all cotton," said Frank Smith, a designer for Evan Picone Sportswear. "It looks better and takes color better. Ramie takes color in a heathered look. You never get a solid red, but a tweedy red." But, Smith uses ramie when designing a sweater for a line of linen clothing. With ramie being a poor cousin of linen, it is used "to give the look and feel of linen" without the cost of linen.

Executives at Liz Claiborne Inc. say ramie gives designers more diversity, particularly in the summer when customers prefer natural fibers. "It's cool and breathes with you," said Dana Buchman, vice president for knitwear design. "You can spin it very very fine or make it chunky and textured, making it easier to make sweaters different from season to season."