Democrats on the House Appropriations Committee voted 25 to 11 yesterday to allow Rep. Robert L. F. Sikes (D-Fla.) who was reprimanded by the House last year for conflict of interest and using his office for personal gain, to remain as chairman of the subcommittee on military construction.

The vote assures a showdown Wednesday when all the House Democrats vote by secret ballot on the committee members' selections for all Appropriations subcommittee chairmen.

Over 50 democrats have signed letters asking their party colieagues to oust Sikes, arguing that retaining him would raise doubts about Democrats' sincerity in wanting to clean up the House and enforce a tougher new code of ethics.

Both Majority Leader Jim Wright, (Tex) and Speaker Thomas P. (Tip) O'Neill (Mass.) have said they would favor retaining Sikes, though yesterday O'Neill admitted it probably would have been "better if I held back."

"I'm not trying to influence the caucus one way or the other." O'Neill said, though he added that he realized that as speaker his words carry some weight. O'Neill said he made his judgement by asking himself whether Sikes "has been found guilty" and whether "he paid for what he did," and said Sikes would carry the "stigma" of his "censure" for the rest of his life.

"I believe the sins of the past should be forgiven." O'Neill said, but added that any future offender would find the "gates of mercy closed."

"It probably would have been better if I had hedged on Sikes," O'Neill said.

Appropriations Committee Chairman George Mahon (D-Tex.) voted to retain Sikes but Said, "It was the feeling of many that a final determination should be left up to the caucus" of all Democrats.

In a letter seeking support. Sikes appeared to be reminding party colleagues that he was the one they turned to for keeping threatened military bases open. "In my work I have made a particular effort to be helpful to all parts of the nation and to assure a military presence with operating bases throughout the country," Sikes said.

The 47 New house Democrats will hold a meeting today on Sikes and his chairmanship.

Sikes was reprimanded by the House Ethics Committee and by the full house for not disclosing certain holdings as required, for helping enact legislation that allowed development of land he had a financial interest in, and for arranging to locate a commercial bank on the Pensacola Naval Air-Station in his district, then buying stock in the bank that made him the third largest stockholder.

If Sikes is defeated on Wednesday, he will probably be the only chairman ousted this year. Three were ousted in 1974.