Roses can be beautiful on the bush but even lovelier when cut and brought indoors. The problem is, for many people they stay fresh and fragrant for only a day or two whereas if left on the bush they may have lasted two or three times as long.

According to researchers who have spent years working on the problem, it is possible for roses to last much longer if a few rules are followed.

When the rose is cut, its life support system is severed, according to Dr. H. Paul Rasmussen, Michigan State University professor of plant physiology. It can no longer get the water and food it needs to sustain life. When put into water, it may not be able to use it.

The cells in the stem of a rose, which carry the water, are like a handful of soda straws. As long as the straws are in a glass of water, you can draw water up through them. Take them out of the water while sucking on the straw, you draw up air.

With roses, the cells in the stem have end plates, or small screens, that allow the passage of water. A small bubble of air is formed and trapped at the end of the rose stem when it is cut from the plant. The life-giving supply of water is cut off, or is seriously reduced, and the rose may wilt or die even if it is placed in water.

Fortunately, blockage of the rose stem is restricted to the first half inch of the stem from the base cut. Cutting the base of the stem removes the block and gives the rose a chance to get rehooked to its life-support system.

To prevent the base of the stem from gulping in another air bubble, the recutting should be done under water. By using a sharp knife or shears, with the base of the stem under water in a pan or sink, you ensure a water supply to the rose.

The cut also can be made under running water. Once the cut is made under water, a small droplet hangs on the cut end, so you can then safely move the stem to the vase with water. Care must be taken that the cut end of the stem doesn't dry off before it reaches its new water supply.

The rose will continue to need food, and that can be provided by adding a flower preservative to the water. Some that are recommended include Floralife, Smithers-Oasis and Burpee's Everbloom. Tests have shown that Sprite, a soft drink, also can be used effectively, according to Dr. Peter B. Pfahl, Penn State University professor of floriculture.

The citric acid and carbonation in the soft drink control the development of microorganisms that can block water-conducting vessels of rose stems and reduce firmness. Sugar in the soft drink sustains life. The recommendation is to mix one part water with each part soft drink and add a half teaspoon of chlorine bleach to each quart of solution. The bleach cuts bacterial growth.

Occasionally a rose will wilt, or develop a weak stem just below the bud, causing the bloom to tip over. Remove that bloom from the arrangement, recut about one inch from the base of the stem under water, then submerge the entire bloom, stem and foliage under water for 20 minutes or so, says Dr. Rasmussen, and you will find the flower revives nicely and can be replaced in the arrangement.

Research has shown that vase life is not lost by letting the flower mature longer on the plant, according to James C. Krone, vice president, Roses, Inc. In fact, he says, there is less chance of the rose opening with a bent neck if allowed to mature further on the bush.

If possible, cut the roses in the morning when they're crisp and they will have to replace less water, says Dr. Cominic Durkin, professor of horticulture and forestry, State University of New Jersey. Put them immediately in lukewarm water (they can't absorb cold water as easily). CAPTION: Picture, no caption