Mortgage-finance giant Fannie Mae's third-quarter profit jumped 16 percent, to $991 million (94 cents a share), from $857.4 million (81 cents) in the same period a year ago.

The rise brought the company's earnings to $2.87 billion ($2.73) for the nine months ended Sept. 30, up 13.6 percent from the $2.53 billion ($2.39) recorded for the corresponding period in 1998.

District-based Fannie Mae is a congressionally chartered, stockholder-owned corporation that buys home mortgages from the original lenders to provide additional capital to the nation's housing markets. Company officials attributed much of the strong performance to growth in the company's mortgage portfolio--which topped the half-trillion-dollar mark during the quarter and is up $89 billion for the year so far. The portfolio growth in turn helped generate an 18 percent annualized increase in net interest income.

At the same time, total credit-related expenses, including costs from foreclosed properties and provision for losses, fell to $20.8 million in the third quarter, compared with $65.3 million in the year-ago quarter.

Fannie Mae said it bought $50.3 billion worth of mortgages in the third quarter, up from $47.3 billion in the year-earlier period. It issued $65.8 billion in new mortgage securities in the third quarter, down from $86 billion a year earlier, and committed to purchasing $37.8 billion of mortgages from lenders, down from $45.6 billion.

* SLM Holding Corp., parent of Sallie Mae, reported a profit of $121 million (75 cents a share) for the third quarter of the year, up from $108 million (64 cents) in the same period of 1998.

Net income for the nine months ended Sept. 30, however, slipped to $359 million ($2.19), from $391 million ($2.29) a year earlier.

Reston-based Sallie Mae provides financial services to colleges and college students, including buying government-guaranteed student loans to provide funds for the education lending market. It holds these loans in its portfolio and also assembles them into packages and sells securities based on them to investors.

Sallie Mae also reported its earnings on a cash basis, in which sales of securities based on student loans are treated as financings rather than sales. Company officials said this treatment eliminates the sharp ups and downs that can result from including such sales in a single quarter. It gives a clearer picture of the company's performance, they said.

On a cash basis, earnings rose in the nine-month period--to $367 million from $332 million--the company said.

* Life Technologies Inc. of Rockville said it earned $9.4 million (38 cents a share) for the three months that ended Sept. 30, compared with $8.8 million (36 cents) for the same period of 1998. For the nine months, Life Technologies said it earned $29.7 million ($1.19), compared with $26.8 million ($1.11) for the 1998 period.

Life Technologies makes products and supplies for life-science researchers, including those working at biotechnology companies.

* FCNB Corp., a bank holding company in Frederick, Md., said that net income for the third quarter fell nearly 81 percent, largely because of expenses related to the acquisition of First Frederick Financial Corp.

The company said that net income for the three months ended Sept. 30 was $598,000 (5 cents a share), down from $3.1 million (26 cents) for the third quarter of 1998.

For the first nine months of 1999, the company had earnings of $6.9 million (60 cents), down 25 percent from $9.3 million (79 cents) for the first nine months of 1998.

Excluding merger expenses, the company's third-quarter earnings for 1999 totaled $3.4 million (28 cents), up 5 percent from $3.2 million (27 cents) for the third quarter of 1998.