A reduction of trash collections in most District of Columbia neighborhoods from twice to once a week is being considered as an energy-saving measure, according to the city's environmental services director.

Herbert L. Tucker, the director, told the mayor's cabinet Friday that he has ordered a study to see what parts of the city would be least troubled by such a cutback.

A similar reduction a few years years ago brought so many protests that twice-a-week collections were resumed.

Tucker told a reporter that the cutback now being considered would be done in neighborhoods where people put most of their trash out for collection only once a week.

The current collection schedule is based upon each resident putting out 60 percent of his trash for the first collection of the week and 40 percent for the second collection, Tucker said.

In much of the city, however, he said more than 85 percent of the trash is put out for the first collection, reducing the need for a second collection. These areas would be cut back under his proposal, he said.

Such a cutback would eliminate the need for 10 to 12 of the 78 collection trucks that are dispatched every day, Tucker said. It also would permit a reduction of the city payroll by about 30 to 40 workers, he said.

At the cabinet meeting, Carroll B. Harvey, acting director of general services, said city vehicles reduced their gasoline usage from 4.9 million gallons in 1977 to 4.2 million gallons in 1978, and the goal for this year is 3.8 million gallons. Harvey said the city is not experiencing gasoline shortages reported by suburban governments.