RCA Corp. said its profits dropped slightly in the third quarter although its television unit, the National Broadcasting Co., began to move up in the television ratings during September after being in third place for most of the past year.

RCA profits for the quarter were $66 million (86 cents a share), down from $70 million (92 cents) in the same quarter last year Sales climbed to a record $1.83 billion from $1.66 billion.

The company said NBC profits declined in the quarter but didn't give figures for the subsidiary. It said declines also were experienced in frozen foods, publishing and carpets, but that color television set sales were strong. f

The results for last year's quarter included a profit of $5.7 million for RCA Alaska Telecommunications, a telephone unit since sold.

For the first nine months, profits were a record $213.7 million ($2.80), including $23 million on the sale of the Alaskan unit. For the same period last year, profits were $203.2 million ($2.66). Sales rose 15 percent to a record $5.47 billion from $4.75 billion.

NBC is off to a strong start in the ratings this fall, having run first or second each week as it emphasized special programs. It had been third last season and during the summer.

The new strength was not reflected in the third-quarter results, but could shoe up in the current quarter if it continues.

RCA has announced it is looking for buyers for its Random House publishing and Banquet frozen foods subsidiaries. It said profits of both units were down for the quarter.

RCA President Edgar H. Griffiths said profits from the consumer electronics sector also were down despite growing color television set sales. He cited rising costs for the company's new video disc system, which hasn't gone on the market, and a decline in profits of RCA's record unit, which was only marginally in the black.

Hertz vehicle rental operations continued to be the company's most profitable subsidiary, but earnings were down somewhat, the announcement said. Earnings were reported up sharply for the company's satellite communications ventures.

Chase Manhattan Corp., which owns the nation's third-largest bank, reported that third-quarter earnings rose more than 60 percent from the comparable quarter last year.

Chase, a holding company whose principal banking unit is Chase Manhattan Bank, said consolidated income before securities transactions totaled $81.2 million ($2.37 a share) in the latest quarter, up 61 percent from income of $50.3 million ($1.41) in the year-earlier quarter.

Net income after securities transactions totaled $77.9 million ($2.27) compared with $49.7 million ($1.39) in the third quarter of 1978.

Nine-month net income before transactions increased to $234.6 million ($6.83) from $138.5 million ($3.92), while net income after transactions was $229.1 million ($6.66), up from $137.2 million ($3.88).

Higher net interest income and increased other operating income were the primary factors in the improved earnings, Chase said.

Meanwhile, the ninth-largest bank holding company, Bankers Trust New York Corp., reported a 39 percent gain in third-quarter profits to $2.36 a share from $1.70 a year ago. Net income was $28.8 million against $21.5 million.

For nine months, Bankers Trust earned $84.3 million ($6.90 a share) against $60.1 million ($4.69) a year ago, a 47 percent gain.

Chairman Alfred Brittain III said higher interest margins and lower loan losses produced the gains, which would have been bigger except for losses on foreign currency translations.

Burlington Northern Inc. reported a 36 percent decline in earnings in the third quarter despite a 32 percent increase in revenue.

BN said third-quarter earnings were $16.5 million ($1.06 a share) compared with $25.8 million ($1.91) in the same quarter last year.

The railroad and natural resources concern said increased costs of fuel, labor and heavy summer maintenance contributed to the decline in earnings. However, improved traffic volume and freight rate increases boosted revenue to $866.6 million from $655 million in the same 1978 quarter.

In the first nine months, BN reported earnings increased 33 percent to $125.6 million ($9.42) from $94.4 million ($7.07) in the first three quarters of 1978. Revenue increased 27 percent to $2.3 billion from $1.8 billion.

A boost in sales of power products, including jet engines, help United Technologies Corp. report a 37.7 percent increase in earnings for the third quarter, the company announced yesterday.

UTC also reported a record business backlog of $10.7 billion up to Sept. 30. The backlog figure -- the first to top$10 billion -- is 46 percent higher than the $7.3 billion as of Sept. 30, 1978. UTC Chairman Harry Gray attributed the backlog to substantial new orders.

Net income in the third quarter was $86.2 million ($1.57 a share) compared with $62.6 million ($1.36) in the comparable 1978 quarter. Sales increased 62 percent from $1.54 billion to $2.49 billion.

Nine-month net income was up 37 percent to $236.5 million from $172.1 million in the first nine months of last year. Sales were $6.1 billion, 33 percent more than the $4.56 billion of the first three quarters of 1978, UTC said. Per-share earnings for the nine months were $4.85 compared with $4.11 for the first nine months of last year.

Wheeling-Pittsburgh Steel Corp., the nation's ninth largest steelmaker, reported a slight improvement in third-quarter earnings over the same period last year.

Net income was $13.57 million ($3.33 a share) on sales of $336.5 million compared with earnings in the third quarter of 1978 of $13.56 million ($3.40) on sales of $304.95 million.

Shipments were 754,639 tons compared with 761,003 tons in last year's third quarters, the company said.

Net income for the first nine months was $41.74 million ($10.33) on sales of $955.87 million. In 1978, Wheeling-Pittsburgh earned $4.08 million (47 cents) on sales of $859.05 million. Nine-month shipments were 2.25 million tons compared with 2.19 million tons in the same period last year.

Signal Cos. had a 39 percent gain in profits from continuing operations in the third quarter even though its biggest division, Mack Trucks, suffered a 30 percent drop in earnings.

President Forrest N. Shumway said Mack had a 12 percent sales gain to $437.2 million in the quarter but its earnings were squeezed by high interest rates and other inflationary factors and by unexpected shortages of components and materials.

The big profit gains were from Garrett and UOP, Signal's two high-technology subsidiaries.

For the company as a whole, third-quarter profits on continuing business were $48.9 million ($1.27 a share) on sales on $1.064 billion, up from $35.2 million (92 cents) a year earlier on sales of $868 million.

Nine-month profits on the same basis were $158.6 million ($3.86) on sales of $3.154 billion compared with $117.4 million ($2.79) on sales of $2.656 billion. Profits on operations since discontinued raised net income for nine months to $4.11 a share from $3.05 a year earlier.

Philip Morris Inc., a tobacco and beverage company, reported a 25.4 percent rise in earnings for the third quarter and nine months.

Per-share earnings for the quarter were up a little less in percentage but were $1.16 on sales of $2.129 billion against 96 cents on four million fewer shares a year ago and sales of $1.817 billion. Net income was $144.42 million against $115.18 million.

Nine-month profits were $384.9 million ($3.09 a share) on sales of $6.14 billion against $307.02 million ($2.55) a year ago on sales of $4.88 billion.

The reason for the larger number of shares and larger volume was the acquisition of Seven-Up Co., whose sales results were fully consolidated only since June 1978. Chairman George Weissman also noted the company's third-quarter investment tax credit was higher.