Social Security Commissioner Martha A. McSteen said yesterday that her agency will send letters today to notify 90,000 people who were removed from disability rolls over the last four years that they may be eligible for reinstatement.

The former beneficiaries will be told to apply immediately for reinstatement under legislation enacted last year, McSteen said. Once they apply, they will begin drawing benefits, at least until the Social Security Administration (SSA) completes a review of their cases under regulations scheduled to be issued in April.

The 1984 law specified that in a wide range of cases, persons on disability rolls may not be removed, even if the SSA thinks they are able to work, unless it can be shown that their medical condition has improved since they first qualified for benefits.

After the agency began an intensive review in 1981 to see whether beneficiaries could work and thus should be removed from the rolls, 18 class-action lawsuits were filed on behalf of 175,000 people who lost their benefits.

In the suits, the plaintiffs argued that the Social Security Act implicitly said that the medical condition of beneficiaries had to improve before they could be removed from the rolls. In 1984, Congress amended the law to make that standard explicit.

McSteen said that all 175,000 people involved in the lawsuits eventually will be notified by certified mail, as soon as the courts return their cases to the agency for reconsideration. So far, she said, 90,000 cases, involving beneficiaries in 21 states, have been returned. She said she expects to send 45,000 more notices soon to people involved in a New York case, then 40,000 more in 10 states including Maryland. Beneficiaries in Virginia and the District are not affected.

The certified letters will include a sentence in Spanish stating, "If you don't understand this notice, please contact your local Social Security office."

But Jonathan Stein, director of Community Legal Services of Philadelphia, said the letters are "grossly inadequate."

He said the letters do not include the phone numbers of local groups that can advise the recipients on how to proceed and do not explain in Spanish that the recipients can be reinstated.