Strong Jeep sales, a general tonign up of its passenger car operations, and a $3 million tax loss carryforward helped American Motors Corp. record a 380 percent year-to-year increase in profits for its third quarter ended June 30.

AMC, smallest of the top four domestic auto makers, said yesterday that earnings for the latest period were $6.1 million (20 cents a share) comiared with $1.6 million (6 cents) a year earlier. Sales rose from $580 million to $703 million during the company's seventh consecutive profitable quarter.

Results for April, May and June gave AMC nine-month profits more than double those for the same period of the previous fiscal year: $10.7 million (35 cents) compared with $5.3 million (18 cents). Sales were $1.9 billion, up from $1.7 billion.

Company officials attributed the improved profits to a number of "fositive steps" the firm has taken since the start of the fiscal year, including:

Expansion of production capacity for AMC's hot-selling four-wheel-drive Jeep vehicles, including conversion of the Brampton, Ont., plant to Jeep assembly.

Assembly from three locations to one operation at Kenosha, Wis., in response to declining sales.

Concentration on smaller passenger cars, including phasing out AMC's poor-selling full-size Matador, and "upgrading" all product lines.

Realignment of the company's top management responsibilities and "revitalization and stabilization" of the AMC dealer organization.

AMC also announced it boosted production at its Kenosha, Wis. plant yesterday to start building 1979 models and was calling back 1,500 employes who had been laid off because of slumping sales. Overtime also is planned this month at Jeep assembly lines in Toledo.

Among major bank holding companies, Citicorp said its second-quarter operating profit rose 27 percent to $137.6 million from $108 million a year ago.

Citicorp, the parent company of Citibnk, N.A., is the world's second largest bank in terms of deposits. As of June 30, total deposits amounted to $60.4 billion, up $7.8 billion.

Per-share operating earnings were $1.11 in the second quarter compared with 86 cents for the same period a year ago, the company said.

In a statement accompanying results, Citicorp Chairman Walter Wriston said lending to multinational corporations accounted for a portion of the profit improvement.

For the six-month period, Citicorp said its operating profit rose to $243.9 million ($1.97 a share) from $200.2 million ($1.60) a year earlier.

Merrill Lynch & Co., parent of the nation's largest securities brokerage house, reported yesterday that second-quarter profits jumped about 80 percent over those of a year ago, largely because of the springtime surge in stock trading volume.

The Merrill Lynch report was similar in tone to those of a number of other major brokerage houses announcing earnings Monday. Among them were the E.F. Hutton Group, whose second-quarter earnings rose nearly 157percent, and Paine Webber Inc., where profits were up 132 percent.

Merrill Lynch, which owns Merrill Lynch, Pierce, Fenner & Smith Inc., said it earled $29.6 million (83 cents a share) in the second quarter on revenues of $408.1 million. Second-quarter net earnings in 1977 had totaled $16.4 million (47 cents) on revenues of $285.1 million.

First half earnings came to $29.8 million (84 cents) against $24.9 million (71 cents) the year before. Revenues rose from $523.5 million in the first half of 1977 to $689.5 million in the first six months of 1978.

Republic Steel Corp. profits rose 41 percent in the second quarter to $31.4 million ($1.94 a share) from $22.2 million ($1.37) during last year's second quarter.

The nation's fourth largest steel producer said sales increased to $910.8 million from $776.8 million.

Republic's six-month profit rose to $41.1 million ($2.54) from $16.03 million (99 cents) as sales rose to $1.74 billion from $1.43 billion in the same period a year ago.

Shipments during the second quarter of 1978 totaled 1.87 million tons, bringing to 3.71 million tons shipments for the first half of this year compared with shipments of 1.84 million tons in the second quarter last year and 3.37 million tons in the first six months of 1977.

Polaroid Corp., the nation's second largest manufacturer of photographic equipment, reported a 28 percent increase in both sales and earnings rose to a record $26.17 million, 80 cents a shar) from $20.47 million (62 cents) a year earlier. Worldwide sales for the period also were a record at $319.69 million, up from $249.27 million.

The company said demand for cameras was exceptionally strong during the period.

Six-month earnings gained 18 percent to $40.65 million ($1.24 on sales of $560.36 million from $34.05 million ($1.05) on sales of $144.11 million during the first half of 1977.

American Cyanamid Co., a diversified manufacturer of chemicals, medical supplies and consumer products, reported flat second-quarter earnings on a hefty increase in sales.

Net earnings for the second quarter were $39.6 million (83 cents a share) compared with $39.3 million (82 cents) for the same period of 1977. Sales were $688.6 million compared with $600.7 million last year, an increase of 14.6 percent.

James Affleck, Cyanamid's chairman and president, said improvements in most of the firm's operations were offset by a decline in fertilizer and pesticide earnings and by higher interest expenses.

First-half earnings rose 7.2 percent to $76 million ($1.59) from $70.9 million ($1.48). Sales totaled $1.34 billion, up from $1.17 billion.

St. Regis Paper Co. said its second-quarter profits rose 38.3 per cent to $39.9 million ($1.25 a share) from $28.9 million (91 cents) during the comparable year-ago period.

The forest products company said revenues for the period increased to $609.8 million from $518.7 million a year ago.

Company Chairman and Chief Executive Officer George Kneeland said the strong second-quarter performance was aided by the absence of "unusual items" which had a negative impact during the first quarter. As a result, the company benefited fully from continued excellent results in printing papers, newsprint, construction products, and oil and gas operations, he said.

For the six months, St. Regis showed an 11.4 percent rise in profit to $55.4 million ($1.73) from $49.8 million ($1.57).

Revenues were $1.131 billion compared with $990.7 million for the first half of 1977.

Northrop Corp. reported net income of $21.5 million for the second quarter, an increase of 30 percent from the $16.5 million earned during the same period last year.

Earnings per share were $1.52 compared with $1.20 during last year's second quarter. Sales were $453 million, up from $741.3. Net income was $40 during the year-ago period.

During the first half of the 1978, Northrop's sales were $887.3 million, up from $741.3. Net income was $40M9 million ($2.90 a share) compared with $31.4 million ($2.31) for the same period last year.

Thomas Jones, chairman and chief officer of the diversified aerospace company, said the higher sales and earnings reflect increased sales of aircraft and business services offered by the company.

Continental Illinois Corp. yesterday reported a 14 percent gain in earnings for the first half of 1978 and said its improved performance was due to increased interest income.

President Roger Anderson said first-half income before security transactions was $79.7 million ($2.23 a share, up from $69.9 million ($1.96) during the same period in 1977. Second-quarter net income was $39.6 million (1.11) 11.7 percent over $35.4 million (99 cents) in 1977.

Net interest income for the half was $282.9 million, up 12 percent from the $252.4 million reported for the first half of 1977.

The firm is parent of Continental Illinois National Bank and Trust Co. of Chicago and is the nation's 11th largest commercial banking company.