The Senate Commerce Committee yesterday approved a measure that would reduce the number of members of the Federal Communications Commission and the Interstate Commerce Commission to five each over the next 12 months.

In the process, the measure would limit FCC nominee Stephen A. Sharp to a term of less than a year, if he is confirmed by the Senate.

Sharp, currently FCC general counsel, faces strong opposition on the committee, which so far has refused to consider his nomination. Sen. Ted Stevens (R-Alaska), who is leading the opposition, has backed Alaska Public Service Commissioner Marvin Weatherly for the post.

The measure approved yesterday also would insure that controversial ICC Chairman Reese Taylor couldn't be reappointed to the agency when his term expires at the end of 1983 unless there is another Republican vacancy available at that time.

For some time, the Commerce Committee has been considering reducing the membership of the two regulatory agencies to five, the number sitting on most federal agencies. By law, the ICC can have 11 members and the FCC seven. The ICC currently has six members and the FCC seven.

Under the measure approved yesterday, introduced by Sen. Harrison H. Schmitt (R-N.M.):

* The term of ICC member Reginald E. Gilliam Jr. would expire at the end of this year, as it does currently, and he would not be replaced.

* Taylor could not be reappointed to the ICC after his term expires at the end of next year because the rule requiring a political balance on the commission would be violated.

* The term of FCC member Joseph R. Fogarty would expire at the end of June 1983, as it does now, and he couldn't be reappointed.

* The seven-year term to which Sharp was nominated also would expire at the end of next June. He was nominated to replace Abbott Washburn, whose term expired at the end of last month.

The result would be that the ICC would have five members at the end of this year, and the FCC would have five members at the end of next June.