Syscon Corp., a computer systems engineering firm based in the District, said its profits for the third period were up 1 percent to $924,000 (30 cents a share), compared with $915,000 (31 cents) in the same quarter last year. Syscon said that the average number of outstanding shares increased between the third quarter of 1983 and the most recent period, accounting for the slightly lower earning-per-share figure.

Revenue grew to $26 million in the June-August period, compared with sales of $21.9 million the previous year.

The company said higher advertising costs and interests costs restrained earnings growth. The interest expense resulted from delays in payments by the federal government, the firm's biggest customer.

For the first nine months of the fiscal year, net income rose to $2.9 million (93 cents) on sales of $77.3 million, from $2.4 million (86 cents) on sales of $60.9 million for the comparable period of 1983.

F&M Bancorp, parent of the Farmers and Mechanics National Bank, reported a 13 percent increase in net earnings for the first nine months of this year.

The Frederick-based company said profits at Maryland's ninth-largest bank rose to $3.4 million ($4.53 per share) from $3 million ($4.12) last year.

Total assets climbed to $331.1 million in for the three quarters ending Sept. 30, compared with $301.4 million for the comparable 1983 period.

Equitable Bancorporation said its third-quarter profits rose 97 percent to $6.9 million (75 cents a share) from $3.5 million (27 cents) in the same period of 1983.

The Baltimore-based bank holding company, which owns three banks with 129 branches in two states, said its net income for the first nine months came to $17.8 million ($1.84), an 82 percent increase over profits of $9.8 million (79 cents) the year before.