A Northern Virginia woman whose husband has been convicted of masterminding an investment fraud pleaded quilty yesterday to failing to file her 1978 federal income tax return.

The tax charge against Sylvia A. Ball, 35, arose out of a lengthly investigation into the activities of her husband, Thomas J. Ball of Great Falls, the former operator of Tom Ball & Associates. Ball, 39, pleaded quilty last month to charges related to a scheme in which the government says he absconded with nearly $800,000 from at least 20 investors.

His wife pleaded guilty to the misdemeanor tax charges in U.S. District Court in Alexandria after prosecutors agreed to drop three felony tax fraud counts against her.

She failed to report $5.540 in rental income for 1978, according to assistant U.S. Attorney Joseph J. Aronica. The prosecutor said she also failed to properly file tax returns for the years 1976 and 1977.

Her sentencing was postponed until July 11. She could receive up to one year in prison and a $10,000 fine.

Ball, who is scheduled to be sentenced in federal court Friday, could receive up to 23 years in prison and a $21,000 fine. He pleaded guilty to two counts of mail fraud, one count of securities fraud, filling a false income tax return and lying to the grand jury that investigated him.

Ball convinced Washington area couples, many of them government and military workers, to invest in securities and land development deals that later turned out to be nonexistent according to the government.

Ball was jailed last month after a Fairfax Circuit Court judge revoked his bond when he pleaded quilty to a state charge for allegedly swindling $20,000 from a Fairfax man in the scheme.