A House subcommittee substantially weakened a proposed statewide minimum housing code today and in effect killed a rental subsidy plan for the poor.

The subcommittee, considering a full package of bills proposed by Gov. Harry Hughes, voted 5 to 1 to give local governments three years to write their own housing codes. The subcommittee said the state should develop a model code that would be imposed only if a county does not adopt one of its own. Currently, four of Maryland's 23 counties have such codes, as do Baltimore and some other municipalities.

Ardath Cade, an assistant secretary of the state Department of Housing and Community Development, said the minimum state code proposed by Hughes would impose standards such as a floor other than dirt, sound walls and a roof, ventilation, an exit and entrance, and, "if possible and over time," electricity and indoor plumbing.

But under the bill approved by the panel, there were no minimum standards. "If you had one light bulb per house and a one-hole privy, and you enforced it, then the state housing code would have no effect," said Del. Thomas Hattery (D-Frederick), who supported the changes.

The subcommittee's vote could be changed by the full Ways and Means Committee, but the highly structured House is usually reluctant to overturn a subcommitee vote. The subcommittee approved other bills in Hughes' housing package, including measures to stimulate low-income housing production, to install indoor plumbing, to subsidize housing for disabled adults, and to subsidize closing costs for low-income home buyers.

Social service advocates said the rental assistance and housing code measures were among the most important proposals. "They cut out the two programs guaranteed to help the very poor," said Ron Halbright, leader of the Maryland Low Income Housing Coalition.

Said Del. Dennis Donaldson (D-Prince George's), subcommittee chairman and the only member from the Washington area voting today, "There are different living standards in the state of Maryland, and the people in those jurisidictions ought to write them and they ought to enforce them."

The subcommittee withstood intense lobbying from administration officials and social service advocates and upheld a decision to delete $1 million for a new program to subsidize rents for impoverished adults.

Advocates of the program had argued that the program would help people who are not covered by any other program, would be cost-effective, and would give recipients a more stable environment than a shelter. But the subcommittee requested that the money be used elsewhere.

Donaldson said the committee believed that "there are programs already out there for the homeless, for families in crisis, and all they've got to do is give them the money." Moreover, Donaldson said, the target population consists of people who might not stay in the room if it was paid for. "There are times they're going to want to be in a shelter, and there are times they're going to want to sleep outside."

The House panel's action is also in conflict with the Senate Finance Committee, which approved the housing package last week. The Senate panel voted, for example, for full implementation of the statewide housing code beginning in 1988, to give local governments more time to fashion their own codes. The senators also voted to require that tenants not be displaced because of the code unless alternate housing is arranged.