International Telephone & Telegraph Corp., the world's largest manufacturer of telecommunications equipment, yesterday reported third-quarter earnings of $197.93 million ($1.35 a share) compared with a $136.39 million loss in the same period a year ago.

ITT reported revenues of $5.63 billion in the period compared with $5.22 billion a year ago.

The New York-based company, ranked 11th among the Fortune 500 largest industrial corporations, has plants and facilities in 80 countries.

It also announced it is raising its quarterly dividend to 65 cents a share from 60 cents, payable Jan. 1, 1981, to shareholders of record as of Nov. 20. fIt was the 17th consecutive annual increase in the diveidend payout, lifting the annual rate to $2.60 a share from the current $2.40.

Meanwhile, Tampax Inc., the nation's largest manufacturer of tampons, said its sale and profits dropped during the third quarter, partly because of publicity about toxic shock syndrome.

For the first nine months of the year, ITT said it earned $608.95 million ($4.17 a share) on revenues of $17.04 billion compared with earnings of $232.14 million ($1.60) a year earler on revenues of $15.49 billion.

Tampax said profits for the quarter fell 27 percent to $9.6 million (85 cents a share) from $13.2 million ($1.17) in the same period of 1979. Sales dropped 6.7 percent to $53.6 million from $57.4 million.

E. Russell Sprague, president of Tampax, said the growth of the tampon industry has been hurt, at least temporarily, by the controversy over toxic shock syndrome, a rare disease that was linked statistically to tampon usage.

Rely tampons, made by Procter & Gamble, were withdrawn from the market after statistical studies seemed to indicate a greater relationship between that brand and the disease.

Sprague said the growth of Rely sales earlier in the quarter and the "adverse publicity surrounding that product's subsequent association with toxic shock syndrome" hurt Tampax sales.

Nine-month profits were down 12.9 percent to $29.6 million ($2.62) from $34.0 million ($3.01). Sales were down by 0.7 percent to $154.6 million from $155.7 million.