RESIDENTIAL REAL ESTATE : Signs of life:

* Carole Eichen, president of Santa Ana’s Carole Eichen Interiors Inc., says she has signed contracts with 14 builders in recent weeks to design 55 model homes in new complexes--most in California but including developments in Las Vegas, Chicago and parts of Florida. While the ups and downs of the model-home design business are not conventional economic indicators, Eichen said, they do “mirror consumer confidence. . . . We’re seeing an upswing in buyer momentum, which is a very positive sign.”

* Warmington Homes in Costa Mesa says it sold nearly 350 houses in 19 Southern California developments in the first half of its 1992 fiscal year. That amounts to more than $50 million in sales.

* Aikens Communities Inc. has begun 24 detached homes and 18 condos in University Hills, UC Irvine’s residential development for faculty and staff.

* Northern Trust Bank of California, based in Newport Beach, has launched a special mortgage loan program for first-time home buyers in the low- and moderate-income brackets, defined as annual family income not exceeding $60,000. The bank says it will waive points and fees, and provide an interest-rate bonus on savings accounts intended for borrowers’ down payments.