A collegial power struggle is under way within the House Armed Services Committee, where Rep. Charles E. Bennett (D-Fla.) wants to trade his long-held chairmanship of the seapower subcommittee to run the procurement subcommittee, chaired by Rep. Samuel S. Stratton (D-N.Y.).

Stratton, however, is telling colleagues he wants to remain as chairman of procurement. Under House rules, the most senior member--in this case, Bennett--expresses his subcommittee preference in a caucus of fellow Democrats, who then vote by secret ballot on whether to grant it. The vote on this is scheduled for Wednesday.

If Bennett gets his wish and goes from seapower to procurement, Stratton would be next in the seniority line to pick another subcommittee chairmanship. His options include seapower and investigations.

Because of retirements, Reps. Les Aspin (D-Wis.) and Ronald V. Dellums (D-Calif.) are in line to get subcommittee chairmanships on the Armed Services Committee. What they get depends on what the more senior chairmen choose.

The subcommittees on military personnel, on readiness and on military installations are the leading possibilities.

As one of the Navy's strongest congressional allies in his role as seapower subcommittee chairman, Bennett has been a champion of the 600-ship fleet.

One reason he wants to change, according to those who know him well, is to broaden his knowledge against the day he becomes chairman of the Armed Services Committee. He is second in seniority among Democrats after Rep. Melvin Price (D-Ill.), 78, the chairman.

If Bennett becomes chairman of the procurement subcommittee, as is likely, he will be in a position to play a major role on the MX missile. He voted against giving President Reagan funds to put the MX into production last year when the Pentagon was advocating the controversial "Dense Pack" deployment scheme now under review.

Price voted for MX production funding.