A House panel appears likely to defeat an effort, backed by members of the Moral Majority and some church groups, to overturn controversial District legislation on insurance for persons who test positive for exposure to the AIDS virus, according to knowledgeable observers.

The House District subcommittee on fiscal affairs is scheduled to hold a hearing and markup session today on a resolution to disapprove the D.C. legislation. Several persons opposed to the legislation were added to the witness list at the last minute at the request of two minority members.

"It looks to us like it's a sham hearing as a prelude to burying the resolution of disapproval," said Gary Curran, director of legislation for the Committee to Protect the Family, which is opposed to the legislation. Curran's group was not among those added to the witness list yesterday.

Members of homosexual rights groups that support the insurance legislation discussed testifying with committee staff, as well, but were told there was no need, according to a top committee aide.

"I think the votes are there to reject the disapproval resolution, based on our reading of the subcommittee," said Johnny Barnes, senior staff counsel to the House District Committee and administrative assistant to D.C. Del. Walter E. Fauntroy, who heads the fiscal affairs subcommittee.

"Assuming they vote it the disapproval resolution down tomorrow, that will probably end the matter in Congress," Barnes said.

The legislation, believed to contain the strongest protections in the country for persons who test positively for exposure to the AIDS virus, prohibits life and health insurers from denying coverage to such persons. The legislation also prevents the companies from charging higher premiums on the basis of such tests for five years.

The legislation does not extend its coverage to persons who have AIDS.

Legislation approved by the D.C. Council and signed by the mayor is subject to a congressional review period before going into law. The AIDS insurance bill is due to go in effect Aug. 6 unless Congress disapproves it within that time, Barnes said.

Since the advent of home rule 11 1/2 years ago, the District Committee has provided almost unbroken support for the city's position on issues. The only resolution of disapproval passed by the committee dealt with a 1979 city bill restricting the location of foreign chanceries, according to Barnes.

That was one of only two resolutions of disapproval to win approval in Congress since home rule. The other related to revisions in the city's sexual assault laws, which were overturned by Congress in 1981 under special rules that do not apply to the bill now under consideration.

The sexual assault bill was defeated under old rules that allowed one house of Congress to disapprove criminal laws under expedited procedures that made it easier for opposing members to get the issue to the House floor.

The AIDS insurance bill is not a criminal code matter, and Congress approved legislation in 1984 to bring congressional veto procedures for the District into line with a Supreme Court ruling outlawing one-house vetoes. Now, any disapproval must be passed by both houses and signed by the president.

The D.C. Council gave its final approval to the insurance legislation in May. Resolutions of disapproval were introduced in Congress last month by Sen. Jesse Helms (R-N.C.) and Rep. William Dannemeyer (R-Calif.).

Opponents of the legislation have argued that it will mean healthy people will have to pay higher insurance costs to make up for added risks taken on by insurers. Some have opposed it as giving special treatment to AIDS-exposed homosexuals.