A 31-year-old Columbia woman who used fake invoices to steal more than $350,000 from a Maryland temporary staffing company over a 2 1/2 -year period pleaded guilty yesterday to felony theft by scheme.

Howard County prosecutors said they will seek a significant prison term - 15 years with all but eight years suspended - for Tiffany F. Powers as a result of the thefts, which continued after she was laid off from Allegis Group last year, according to court documents.

Powers' sentencing is scheduled for Jan. 31 before Howard Circuit Judge James B. Dudley.

Powers, of the 9400 block of Kilimanjaro Road, had been working for Hanover-based Allegis for three years when the thefts started in November 1999, according to charging documents. She also filed for bankruptcy that year, said Assistant State's Attorney Lynn Marshall.

By the time company officials discovered the scheme this year, 89 checks based on fake invoices and made out to Powers Catering had been sent to two post office boxes belonging to Powers and her husband, Wayne, according to court documents.

Powers, who was a human resources representative, had authorization approval over invoices while she worked at the company, Marshall said. Powers continued to fax invoices with approvals using the name "Karen Smith" - a fictitious Allegis Group employee she had created - after she was laid off in September last year, Marshall said yesterday. The largest of the payments to Powers Catering - $31,000 - was made in November last year, the documents show.

In all, Powers, who was making $28,500 as a salaried employee, stole $366,053 from the company, Marshall said.

Charles L. Fuller, Powers' attorney, said he would not comment on why his client took the money or how it was spent until after her sentencing.