Citing a $68 million write-down of its Polavision instant movie inventory, Polaroid Corp. announced yesterday that it lost $23.1 millin in the third quarter.

Polaroid President William J. McCune, Jr. said the instant-camera produced suffered a 70-cent-a-share earnings loss during the third quarter compared with a 1978 third-quarter earnings of $3494 million ($1.04 a share).

McCune keyed the loss to the company's decision six weeks ago to mark down the inventory value of its Polavision products -- an instant movie system that has suffered slow sales since it was introduced several years ago. He said the entire write-down has been charged to the third quarter.

Without the revaluation, third-quarter earnings would have been 48 cents a share McCune said.

Polaroid sales for the quarter were $348 million, a 2 percent increase over 1978 third-quarter sales of $341.7 million.

Sales for the first nine months of 1979 were $934.8 millin, up 4 percent from $902.1 million in the first three quarters of 1978.

But earnings were $7.3 million (22 cents), a sharp drop compared with $75 million ($2.28) for the first three quarters of 1978.

Lockheed Corp., which alredy had announced substantial write-offs on its L-1011 TriStar aircraft, reported third-quarter earnings of $1.1 million, down sharply from the $10.6 million recorded in last year's third quarter.

Lockheed Chairman Roy A. Anderson announced Oct 2 that the aerospace giant was experiencing higher-than-expeced costs on current Tri-Star production and would write off these expenses in the third quarter.

The $1.1 million earned in the third quarter of 1979 actually resulted in a per-share loss of 2 cents on both a primary and fully diluted basis, because of preferred stock divident requirements and provisions for stock redemptions. Lockheed's per-share earnings in the third quarter of 1978 were 63 cents.

Lockheed earned $22.8 million ($1.30 a share) in the first nine months of the year compared with $38.4 million ($2.43) in 1978.

Kroger Co., the nation's second largest supermarket chain with 1,200 stores in 21 states, reported a 16 percent rise in sales and 10.5 percent increase in earnings for the third quarter.

Sales for the 16-week period ended Oct 6 totaled $2.791 billion, an increase of $384.5 million over sales of $2.407 billion for the comparable period last year. Earnings were $26 million (94cents a share) compared with $23.5 million (83 cents) in the 1978 third quarter.

Forty-week sales were $6.78 billion, up 16.2 percent from sales of $5.832 billion for the same period last year. Earnings were $72.9 million ($2.66), a 33.8 percent increase over $54.5 million ( $2) last year.

Procter & Gamble Co. announced record earnings of $185.7 million ($2.25 a share for its fiscal first quarter.

In the comparable quarter last year, the company reported net income of $166.9 million ($2.02).

Worldwide net sales were $2.66 billion, a 17 percent increase over sales of $2.29 billion for the similar period in 1978.

Xerox Corp. reported record third-quarter and nine-month revenues and profits, saying sales were strong both for its small and large copiers.

Earnings for the third quarter were $137.7 million ($1.71 a share), up from $134.7 million ($1.67) in the 197, third quarter. That period included a one-time, before-tax payment of $25 million received as part of an agreement exchanging patent licenses and ending litigation between Xerox and IBM.

Excluding the $25 million payment, net income in the 1978 third quarter was $122.7 millin ($1.52).

Revenues for the quarter were $1.76 billion, an increase of 16 percent from the $1.51 billion for the same period a year earlier.

Nine-month revenues totaled $5.042 billion, 16 percent above the $4.34 billion for the comparable period of 1978.

Net income was $424.3 million ($5.27) compared with $368 million ($4.57). Excluding the IBM payment, the 1978 figures would be $356 million ($4.42).

The acquisition of a steamship company and steady performances from other operations offset a slowdown in steel revenues for LTV Corp., which reported third-quarter net income of $33.1 million ($1.12 a share) compared with $3.8 million (22 cents) in the third quarter of 1978.

LTV's consolidated sales for the third quarter were $2.03 billion, up from $1.30 billion in the comparable 1978 quarter.

This year's results reflect the acquisition of Lykes Corp, a shipping firm, the company said.

In the first nine months, LTV earned $113.9 million ($3.93) on sales of $6.04 billion compared with profits of $3.08 million ($1.98) on sales of $3.87 billion in the 1978 period.

General Foods Corp. reported a 51.3 percent gain in second-quarter earnings on a sales rise of 7.2 percent.

James L. Ferguson, chairman and chief executive, said the earnings growth reflects the strengthening of grocery coffee business.

Net income for the quarter ended Sept. 29 was $74.87 million ($1.50 a share), up from $49.49 million (99 cents) in the comparable quarter last year. Sales advanced to $1.381 billion from $1.289 billion a year ago.

First-half net income jumped 35.2 percent to $143.74 million ($2.88) from $106.29 million ($2.13) for the same period last year.Sales rose 9.1 percent to $2.878 billion from $2.639 billion the year before.