NEW YORK (AP) _ A former Drexel Burnham Lambert Inc. trading assistant was sentenced today to 10 months in prison for lying to the government during its investigation of the Wall Street firm.

The punishment was eight months less than Lisa Jones received at her original sentencing last year. That term was thrown out by a federal appeals court that said the sentence was longer than prescribed by federal sentencing guidelines.

U.S. District Judge Leonard B. Sand also ordered the one-time teen-age runaway who climbed to a $100,000-a-year job at Drexel to pay $25,000 in fines plus the cost of her incarceration.

Jones, 27, was convicted by a federal jury in March 1989 of seven counts of perjury and obstruction of justice for lying to a federal grand jury investigating trading activities at Drexel.

She was the first person convicted in the government's lengthy investigation of fraud on Wall Street.

Prosecutors showed at her trial that Jones handled transactions that constituted illegal ''stock parking,'' which involves hiding the true ownership of securities. Jones had denied any knwowledge of such transactions.

Jones worked at Drexel's Beverly Hills, Calif., junk bond department as a trading assistant to Bruce Newberg, who was convicted last year of parking and other charges and sentenced to three months in prison.

Newberg reported directly to Michael Milken, the ex-head of Drexel's junk bond department who pleaded guilty to six felonies earlier this year to settle wide-ranging securities fraud charges.

The 2nd U.S. Circuit Court of Appeals in March ruled that Sand wrongly gave Jones a sentence greater than the 10- to 16-month term recommended by new sentencing guidelines governing crimes that occurred after January 1987.

Sand originally had added on to the term on grounds that Jones' perjury had severly impeded the government's Drexel investigation.

Sand said today that Jones' perjury was ''not a sudden impulse. It was a persistent conduct of perjury on several occasions despite warnings'' from the government.

Jones, who sobbed throughout the 90-minute sentencing, was ordered to continue to receive mental health therapy during her term. She is to report to a minimum-security prison camp in Phoenix in 30 days.