A former Northern Virginia financial planner was sentenced to six years in federal prison yesterday for an investment fraud scheme in which prosecutors said he absconded with nearly $800,000.

Thomas J. Ball, former operator of Tom Ball & Associates, said in court yesterday that he was sorry for his misdeeds.

Ball, 39, of Great Falls, pleaded guilty in U.S. District Court in Alexandria last month to five felony charges in which he admitted that the land development securities deals he promised to his clients were nonexistent.

The investors, many of them military and government workers, lost money that they had planned to set aside for their retirement and their children's educations, according to assistant U.S. Attorney Joseph J. Aronica.

Ball pleaded guilty to two counts of mail fraud, one count of securities fraud, filing a false income tax return and lying to the grand jury that investigated him.

Ball is also waiting sentencing in a Fairfax County case in which he pleaded guilty to a state charge of false pretense for swindling $20,000 from a man in the investment scheme.

U.S. District Judge Albert V. Bryan Jr. yesterday ordered Ball to serve his federal sentence consecutively with any state prison term he might receive.

Ball's wife, Sylvia A. Ball, 35, pleaded guilty in federal court earlier this week to a misdemeanor charge of failing to file her 1978 income tax return. The charge grew out of the investigation of her husband. She will be sentenced July 11.