Mary Treadwell, former head of the D.C. Youth Pride job training program, reported yesterday to the federal prison for women at Alderson, W.Va., to begin serving a three-year term for conspiring to defraud the U.S. government in connection with the management of the Clifton Terrace Apartments here.

An Alderson prison official said last night that Treadwell reported at 6 p.m. yesterday to begin the term, which was imposed along with a $40,000 fine after her 1983 conviction.

A three-judge federal appeals court panel upheld the prison sentence in May, and a request for a rehearing before the entire court was turned down, prosectors said yesterday.

Treadwell, a former wife of D.C. Mayor Marion Barry, was found guilty of conspiring to defraud the federal government and the tenants of Clifton Terrace, a low-income apartment complex on 13th Street NW, of thousands of dollars to enrich herself.

She was convicted also on seven counts of making false statements to federal officials about the management of the apartment but was acquitted on 13 other charges.

The jury deliberated for 131 hours over 17 days before reaching its verdict.

P.I. Properties, a corporation set up to buy Clifton Terrace from the federal government, was headed by Treadwell. The company owned the apartments from 1974 to 1978.