Five persons, including two former trust officers at Riggs National Bank, pleaded guilty yesterday in federal court here to conspiracy charges stemming from a fraud scheme involving $9.6 million in improper federally insured mortgages.

The five defendants, one of whom also pleaded guilty to a bribery charge, are for the most part lesser players in the scheme that U.S. Attorney Joseph E. diGenova said reaped some of them "hundreds of thousands of dollars."

DiGenova said that the five defendants -- who also include a real estate broker, a real estate salesman and a loan officer of a mortgage company -- were involved in securing FHA-backed loans for 153 properties in the District, mostly two- and four-unit low-income housing, based on appraisals far in excess of their actual worth.

The bloated appraisals were used to secure loans much larger than the true cost of the units, permitting the buyers not only to finance their down payments and closing costs with the loans but also to have cash left over when the transaction was completed. More than $3 million of the loans is in default or foreclosure.

At least five other persons were involved in the scheme, diGenova said, and one of them got at least $1 million from the transactions.

"There are a substantial number of individuals who are under investigation and will be charged," said diGenova, but he refused to name the primary targets of the probe.

Assistant U.S. Attorney Steven C. Tabackman, outlining the scheme to U.S. District Judge Harold H. Greene, identified the five other participants in the scheme as Steven Madeoy, Marvin Gitelson and Jack Spicer, real estate investors; Jakey Madeoy, a Veterans Administration-approved appraiser; and Michael J. Friedman, a lawyer.

The five also were named in documents filed in court in support of the guilty pleas. None of the men has been charged.

As part of their plea agreements, all five defendants are expected to testify at any future trial arising from the ongoing investigation. The pleas are the first major development in the government's lengthy investigation, which was initiated more than a year ago by the inspectors general of the Department of Housing and Urban Development and the Veterans Administration.

The scheme, which began in late 1981 or early 1982, apparently was spawned by that period's disastrous real estate market, which was not attracting legitimate buyers for such low-income property, a HUD official said.

Yesterday's pleas came more than a year after FBI agents searched the upper Wisconsin offices of United Properties, a real estate brokerage firm, and seized 20 boxes of documents related to the fraudulent loans.

Two of the men who pleaded guilty were principals in United Properties. They are real estate broker Ritchie Gaylen, 51, now of Jacksonville, and the firm's real estate salesman Lynn Martin Wall, 43, of 2800 Center Ridge Rd., Oakton.

Gaylen pleaded guilty to a conspiracy charge and a bribery charge. Wall pleaded guilty to a conspiracy count.

Also pleading guilty to conspiracy were:

Patricia H. McAdams, 47, of 4201 Enterprise Rd., Bowie, formerly a loan officer at Cameron-Brown Co. and Marathon Mortgage Corp.

Harriette T. McGinnis, 49, of 2509 Branch Ave. SE, a former trust officer at Riggs National Bank and a former treasurer of the District of Columbia Retirement Board.

Gail M. Hartmann, 66, of 500 Heather Ridge Dr., Frederick, Md., a former Riggs trust officer. Hartmann and McGinnis also operated a real estate management firm, Chadwick Inc.

If convicted, each of the defendants faces a maximum prison term of five years and a fine of $250,000, twice their personal gain from the scheme or twice the government's loss, whichever is greater.

Gaylen also faces a maximum 15-year prison term and $10,000 fine on the bribery charge.