Two Virginia state senators who collected $44 a day in tax-free expense payments while they were ill and unable to attend legislative sessions in Richmond said yesterday they were returning the money to the state treasury.

Sens. Paul W. Manns (D-Caroline), who missed the entire 52-day session this year, returned $1,953, and Fred T. Gray (D-Chesterfield), who suffered a heart attack during the 1976 session, returned $792, according to Senate Clerk J. T. Shiropshire.

The action brought to three the number of legislators who have returned a portion of their expense allowances because of questions raised about a Virginia law that legislative clerks have said "mandates" the payments regardless of whether the legislators come to Richmond.

Earlier, Del. Robert E. Harris (R Faifax) returned $1,056 to the state, representing payments he received for the final 24 days of the session when he was in Northern Virginia with a leg fracture.

Manns said he was keeping $335 from the total of $2,288 he was paid in expense money during the session, because that represented a deposit he lost on a Richmond apartment that he had planned to occupy. He became ill shortly before this year's session began.

Both Manns and Gray said they had concluded it would not be proper to keep the money. A joint House-Senate rules committee has yet to decide if the payments should be continued to ailing legislators as well as Richmond-area legislators who live at home during the session.