NEW YORK — Courtaulds PLC, which for the past 10 months has been working to expand production capacity for Tencel, is now giving the 2 1/2-year-old cellulosic a certification program and a new logo.

The certification program, which applies to fabrics made of at least 50 percent Tencel, is being presented to Tencel customers beginning next week, said Ellen Flynn, Courtaulds’s director of marketing for the Western Hemisphere.

Fabric mills wishing certification for their Tencel fabrics will be asked to submit a four-yard sample, two yards of which will be tested for any performance claims — including washability and shrinkage control — while two will be earmarked for Courtaulds’s fabric library.

The certification program is beginning even as Courtaulds continues to await final approval of the generic name for the fiber, lyocell, from the Federal Trade Commission. Under the certification rules, mills and manufacturers must label all fabrics and garments made from lyocell — even those using the brand name Tencel — with the fiber’s interim generic name: CF0001.

“We have positioned Tencel as a luxury fiber, and this is one way to guarantee that customers are receiving the characteristics and qualities that are associated with Tencel,” said Flynn, who, along with Don Vidler, Tencel marketing manager, outlined the plan at Courtaulds’s sales and marketing offices here last week. Courtaulds, which began commercial production of Tencel in July 1992, has roughly three dozen mill customers.

At the same time, Courtaulds is unveiling a Tencel logo that will begin appearing in advertisements in November, and on eligible fabrics and apparel shortly thereafter.

The logo, an X with the word “Tencel” underneath it, was created to highlight the “X-factor that Tencel brings to clothes in terms of drapability and feel,” Flynn said, referring to the fiber’s distinctive characteristics.

The logo will be in black and gray — a black X and lettering on a gray ground or vice versa. The present logo has the word “Tencel” in white on a blue ground.

Flynn and Vidler said the company toyed with the idea of making the logo multicolored, “but we’re doing it in black and gray now to insure that it will go with just about any other label on the garment, and won’t interfere with color in advertisements.”

A colored logo, they said, might be developed later.

The certification and logo programs are the biggest marketing push Courtaulds has put behind Tencel since announcing it was increasing worldwide capacity for the fiber, now at slightly more than 40 million pounds.

Last year was the first full year of Tencel production at Courtaulds’s plant in Axis, Ala., the company’s only full-scale commercial production facility for lyocell. It has a small plant in Grimsby, England, whose output is primarily for research and development. Sales last year for Tencel were close to $150 million.

In November 1993, Courtaulds said it was investing $134 million in expanding the Axis facility, which will increase the company’s current Tencel production from 40 million pounds to 100 million pounds. The expansion, which began in January, is expected to be completed next August.

Then, this past May, Courtaulds announced plans to build a $130 million Tencel plant in Europe within two years, to increase worldwide capacity for the fiber to 150 million pounds. At the time, Sipko Huismans, Courtaulds’s chief executive officer, said four potential sites had been identified — two in the U.K. and one each in Spain and Germany. The site has not yet been finalized.

In addition, Courtaulds is investigating possibilities for Tencel production in the Far East, although no timetable or site has been set.

Huismans said that with the opening of a European plant, sales of Tencel could be between $375 million and $400 million by the end of 1996.