DENVER, Dec. 26— A snow-inducing bacterium is being tested by at least four Colorado ski resorts to determine whether it would augment standard snow-making methods on the slopes.

The maker of a product that uses the bacterium, Pseudomonas syringae, says it produces more snow than standard snow-making methods and at warmer temperatures.

The product is called Snomax and it is made by Advanced Genetic Sciences in Berkeley, Calif. Snomax is the first commercial product of A.G.S., which is primarily involved in research, according to Doug Sarojak, the concern's director of marketing and product development.

Mr. Sarojak said officials of the concern ''are very enthusiastic'' about Snomax, which they believe will permit resorts to lengthen the ski season. The season now runs from late November to early April in Colorado.

''We're talking about an improvement in the efficiency of snow making of from 20 to 80 percent,'' Mr. Sarojak said. ''More snow can be produced at temperatures warmer than with conventional snow-making.'' Scientist Expresses Concern

However, a scientist has raised questions about whether the bacterium might be carried great distances by the wind and damage crops that are sensitive to frost.

Mr. Sarojak said Pseudomonas syringae was a bacterium that did not cause disease among humans and was commonly found on leaves and flowers and other broad-leaf plants, fruits and vegetables. He said people came in contact with it frequently.

The bacterium forms tiny ice crystals that do not harm the plants on which they are found naturally, Mr. Sarojak said. Scientists do not know why they form.

In the snow-making application, A.G.S. uses bacteria that are dead but retain their ice-forming property, Mr. Sarojak said. Large concentrations of the microbes are injected into underground snow-making pipes at a rate so that every drop of water comes out with an ice nucleus around which snow can form, Mr. Sarojak explained. In the standard snow-making process, only water is used with compressed air.

Snomax has been used by the Copper Mountain resort over three winters and has offered enough promise to lead another resort, Breckenridge, to start testing it this skiing season. Two others, Vail and Steamboat Springs, said they planned to add it to their standard snow-making process on a trial basis this winter. Effectiveness Is Mixed

So far, the effectiveness of Snomax has been mixed. At the Breckenridge ski area, high winds caused problems in the first experiment this fall and ''it didn't produce the results we anticipated,'' said Jeff Keener, the resort's snow-making manager.

At Copper Mountain resort, however, testing was more successful.

Rob Scholl, the mountain manager at Copper Mountain, said: ''It's doing what we think it's supposed to do. We think it's working well. We know it helps make more snow. But everytime we test the wind comes up and we can't get a feel for how much more snow is made.''

Mr. Scholl said the resort had completed its tests for this year and he did not know if the product would be used when the weather turns warmer in the spring. Professor Raises Questions

Meanwhile, Prof. Anne Vidaver, the head of the department of plant pathology at the University of Nebraska in Lincoln, has questions about the possible effect of the bacterium if it should spread beyond the resorts to agricultural areas.

''My concern is about when they will be using P. syringae,'' said Professor Vidaver. ''They'd be applying it when the surrounding agricultural areas are most susceptible - in the spring and fall, and there is the possibility that it could be carried by the wind great distances to frost-sensitive crops.

''The information about wind effects is not available,'' said Professor Vidaver. Since the bacterium occurs naturally and is not genetically engineered, she said, ''There is no supervision or review required of its use.''

''Theoretically there is a lot more potential for damage, even though it's not engineered,'' said Professor Vidaver. ''The potential comes from the high concentrations that will be used. I find it ironic that genetically engineered substances are receiving all the attention.''

Professor Vidaver said she thought the fact the bacteria would be dead when applied did not reduce the risks since the ice-nucleation mechanism would still have to be intact for it to work.

Addressing concerns about the use of the bacteria for snow-making, Mr. Sarojak said: ''All along in these developments we have assessed all the risks, to ourselves, and to our families and have determined there are none. As scientists, we're more concerned about the environment than the average person. This is not something we have pulled out of a black hat.''