IMAGINE year-round vegetables that are attractive, tasty, and nutritious. Juicy and flavorful tomatoes or fresh yellow squash to lighten the gloom of a winter storm.
For years this has been the goal of researchers as they worked toward genetically engineered crops of a better quality than those that evolved naturally or were bred through traditional means.
The first such crops may get federal government approval for marketing within a few months. But the means of developing them - genetic manipulation - is a controversial one whose full environmental impact has not been determined.
While boosters are enthusiastic about the potential for ``transgenic'' plants, critics urge a go-slow approach in light of possible unknown effects from the plants.
The Union of Concerned Scientists (UCS), a nonprofit research and advocacy group, recently warned that ``commercialization of transgenic crops poses serious environmental risks.''
Among the risks cited in a report by UCS scientists Jane Rissler and Margaret Mellon is the possibility that such crops could either become weeds or transmit new genes to wild plants that could become weeds. Either scenario, they say, would mean greater reliance on agricultural chemicals.
Dr. Rissler, a plant pathologist and former biotechnology project manager at the Environmental Protection Agency (EPA), cautions against ``a tremendous number of applications to commercialize transgenic crops ... with no adequate regulatory structure to protect against their potential ecological risk.''
Under traditional breeding methods, related organisms are crossed - apples with apples - to emphasize desired traits. Biotechnology allows mixing a wide range of genes, hence the term ``transgenic.''
The United States Department of Agriculture (USDA) has received applications to field test engineered plants that use chicken genes to increase disease resistance in potatoes, flounder genes to reduce freezing damage in tomatoes, and bacteria to reduce insect damage in rice.
Among the transgenic plants now under development, according to the UCS, are corn, cotton, cranberries, soybeans, eggplant, and sugar beets.
In their report, Rissler and Dr. Mellon acknowledge: ``Genetically engineered crops are not inherently dangerous,'' and they don't dispute the safety record of initial testing.
``But the safety record of small-scale field tests, as welcome as it is, does not necessarily predict safety at a commercial scale,'' they write.
Among other potential problems, Rissler and Mellon note: ``Plants engineered to contain virus particles will facilitate the creation of new viruses.'' Transgenic plants designed to produce drugs or pesticides, they warn, could harm other plants and animals.
``What will it mean to have a steady stream of animal and microbial genes entering the gene pools of plants in wild ecosystems?'' they ask. ``It may mean little. But, as yet, it is not clear that we even have the framework within which to ask the question.''
Other scientists dispute these findings. Susanne Huttner, director of biotechnology research at the University of California at Davis, argues that genetic engineering allows for more precise and reliable genetic changes than does conventional crossbreeding.
``That precision and reliability enhances our knowledge of the kinds of modifications that are being introduced into crop plants and, in turn, enhances our ability to make risk assessments and develop risk-management strategies,'' Dr. Huttner writes in an analysis of the UCS report.
Regarding genetic contamination, she notes a 1989 National Academy of Sciences study that found: ``When problems occur, they have been manageable, and, for the most part, confined to the managed ecosystem.''
``In more than 400 carefully monitored field trials in the US and 600 trials worldwide,'' Huttner adds, ``there has been no evidence of any unexpected or unwanted behavior by a genetically engineered plant.''
There is considerable commercial interest in genetically designing marketable crops. During the past five years, most USDA applications to field test transgenic crops have come from chemical, seed, and food firms. (This, in itself, makes critics suspicious.)
``Generally, it's an application the food industry looks forward to benefiting from,'' says Libby Mikesell, communications director at the International Food Information Council.
Contrary to what critics assert, advocates of transgenic crops say the result could be a reduction in the use of pesticides and fertilizers. The food-information council is promoting ``environmentally friendlier squash plants ... that do not require chemical sprays to combat viruses.'' And by the end of the decade, the industry association predicts: ``Consumers will enjoy better flavor and quality,'' as well as a year-round supply, no matter where they live.
Despite the warning of UCS scientists and others, federal agencies like the USDA and the EPA seem content with current regulations applying to ``designer'' crops.
It seems likely that transgenic tomatoes, squashes, and other products will soon be seen in the produce sections of local food stores.