Rep. Robert L. Sikes (D-Fla.), has enlisted the support of defense contractors, retired military personnel and manufacturers in an intense lobbying campaign to help retain his chairmanship of the Military Construction Subcommittee of the House Appropriate Committee.

The caucus of House Democrats will meet today to vote on whether Sikes should retain his chairmanship of the subcommittee, which doles out about $3.5 billion a year for military bases, warehouses, hospital clinics, service clubs and post exchanges, military maintenance and construction.

The opposition to Sikes is strong and the vote is expected to be close. Sikes was reprimanded last year by the House ethics committee and the House for violating standards of conduct. He was accused of failing to disclose holdings in Fairchild Industries, a defense contractor, and helping to establish a bank on the Pensacola Naval Air Station then becoming the bank's third-largest stockholder.

Four congressmen said yesterday they had been called or contracted on Sikes' behalf by retired military personnel, defense contractors or others from their districts.

Rep. Mark Hannaford (D-Calif.) said a local defense contractor, whom he declined to name, had called him on Sikes' behalf. "In my view, I do not think the contractor was behaving improperly . . . But it is obvious to me Sikes is using this to save his seat," Hannaford said.

Rep. Max Baicus (D-Mont), a member of the Appropriations Committee who had signed a letter asking for Sikes' ouster, said a friend from his district had called on behalf of defense contractors.

Rep. Robert Cornell (D-Wis.) said he had no military bases in his district but had been contacted by two retried military officers living there.

And Rep. Eunler Derrick (D-S.C.), was contacted by a retired military officer and a silk manufacturer in his district.

One ominous development for Sikes was that Rep. Edward J. Patten, a 71-year-old New Jersey Democrat slated to become chairman of the subcommittee if Sikes were defeated, suddenly decided to get off the subcommitte.

The move surprised many members of the committee and had the effect of making it easier to vote against Sikes, because doubts about Patten's ability to be a competent chairman have occasionally been raised as a reason for not to vote against Sikes.

Patten said he made the choice because he wanted to stay on both the Labor-HEW subcommittee and the Treasury-Postal Service general government subcommittee. A new rule limiting members to two subcommittees forced him to make the choice.

But the move was considered surprising because most members would rather chair a subcommittee, especially one with the obvious benefits the Military Construction Subcommittee has to dole out.

There was speculation that pressure had been brought to bear on Patten to step aside but sources close to Patten denied it. His leaving the subcommittee places a moderate liberal, Rep. Gunn McKay (D-Utah) in line for the chairmanship in terms of seniority.