Aided by a strong Christmas selling season, two catalog retail companies based in Maryland and Virginia have reported substantial gains in sales and profits for the quarter and six-month periods that ended in late December.

Best Products Co., of Richmond, yesterday reported that profits for the three months ended Dec. 31 rose to $15.3 million ($2.63 a share) compared with $11.8 million ($2.03) in the 1976 period. Sales rose to $251.5 million from $198.1 million.

That brought six-month earnings to $18.4 million ($3.15 a share) on sales of $33.9 million compared with profits of $13.8 million ($2.39) and sales of $261 million a year earlier.

W. Bell & Co., a smaller catalog retailer based in Rockville, reported a 73 percent increase in profits for the quarter ended Dec. 24. Earnings totaled $1.07 million ($1.12 a share) compared with $618,000 (65 cents) as sales rose 27 percent to $25 million.

For the six months ended Dec. 24, Bell profits rose 98 percent to $1.1 million ($1.15) vs. $553,000 (58 cents), and sales increased 32 percent to $33 million. President Walter Bell said the sales and earnings were the highest in the firm's history. Bell is planning to open its fifth and sixth area outlets next fall at Tysons Corner and Springfield Mall.

Wheat First Securities, a Richmond investment firm, had forecast as recently as Dec. 12 that Best and Bell sales gains for the month would be about 22 percent and 12 percent respectively. The actual gains were about 32 percent and 28 percent. Wheat said sales are "very strong" in the final two weeks before Christmas.

Smith's Transfer Corp., a big trucking firm based in Staunton, Va., reported 1977 profits of $9 million ($3.59 a share) compared with $8.3 million ($3.32) the previous year. Revenues rose to $193 million from $166 million.

Fourth-quarter profits, adversely affected by startup expenses in new markets and three new plants, fell to $2.7 million ($1.06) from $3.1 million (1.23), as revenues increased to $63 million from $54 million.

Black & Decker Manufacturing Co., a Maryland tool manufacturer, reported higher earnings and announced an increased dividend. Earnings fro the first fiscal quarter ended Dec. 25 rose 22 percent to $15.4 million (37 cents a share) compared with $12.6 million (30 cents). Sale were up 16 percent to $238 million.

B&D directors approved a quarterly payout of 15 cents a share (up from 12 cents), payable March 24 to owners of record March 10.

Solon Automated Services, a Washington owner of coin-operated laundry facilities, reported profits of $3.57 million ($1.25 a share) in the year ended Sept. 30 compared with $3.44 million ($1.15) the previous fiscal period. Sales rose to $48 million from $43 million.

For the fourth quarter alone, Solon earned $1.08 million (38 cents) vs. $909,000 (32 cents) as sales rose to $13 million from $11 million.

Flow General Inc., of McLean, said its net income for the six months ended Dec. 31 increased 45 percent from $473,000 to $685,000.

Earnings per share grew only from 43 cents to 45 cents, because of issuance of 265,000 shares to acquire minority interest in a subsidiary and other diluting effects of options and warrants.

Flow General, which also has major facilities in Rockville, said sales for the first half of the year increased 14 percent, from $20 million to $22.8 million.