ITT Corp.'s third-quarter profits fell 33 percent to $77 million (50 cents a share), but the conglomerate said yesterday its year-to-year profits would have risen 27 percent except for a one-time gain in the year-earlier quarter.

Also yesterday, People Express airline reported record third-quarter earnings and MCA, the entertainment conglomerate, said profits were up more than 90 percent.

ITT, which is in the middle of selling $1.7 billion in assets to improve its bottom line, said its income was improving in all businesses except telecommunications equipment, which suffered from high costs and weak markets.

ITT's earnings in the three-month period ended Sept. 30 compared with profits of $115.6 million (77 cents) in the third quarter of 1984. The year-earlier quarter was boosted by a one-time gain of $54.7 million (36 cents).

Third-quarter revenue was $4.9 billion, up from a restated $4.7 billion in the third quarter of 1984. Revenue was restated to reflect the sale of numerous businesses in the last year, including Continental Baking Co. and 12 industrial companies.

ITT said its profits for the first nine months of 1985 totaled $308.3 million ($2.03) compared with $273.2 million ($1.81). Revenue for the first nine months totaled $14.7 billion, up from a restated $14 billion during the same period last year.

*People Express Inc., one of the first budget airlines, announced record third-quarter earnings of $16.5 million (55 cents per share) compared with $6.8 million (20 cents) in the same period of 1984.

Net income for the first nine months of 1985 was $10.7 million (10 cents) compared with $10.6 million (34 cents) for the same period in 1984.

"The company is extremely pleased with the record results for the quarter. It is especially gratifying to have results such as these in spite of the negative impact of Hurricane Gloria in September," a company spokesman said. The official estimated the hurricane cost the company in excess of $3.5 million in lost revenue and increased costs.

Third-quarter operating revenue was $269 million, compared with $174 million in the 1984 period. Operating expenses during the same periods were $237 million and $157 million respectively.

Operating revenue for the first nine months of 1985 was 707.3 million, up from $418.4 million in 1984. Operating expenses for the first nine months of 1985 were $656.2 million, up from $384 million in 1984.

The company has 24.2 million shares outstanding.

*MCA Inc. reported third-quarter earnings soared by 90.7 percent to the second-highest level in the company's history.

A major factor in the turnaround was the box-office success of the movie "Back to the Future." MCA's Universal Studios subsidiary had been beset by a string of unsuccessful films.

For the three months ended Sept. 30, the company earned $67.5 million (91 cents per share) on revenue of $626.7 million, compared with profits of $35.4 million (49 cents) on revenue of $412.7 million a year earlier.

MCA's net for the nine months rose by 28.5 percent to $98.2 million ($1.33) compared with $76.4 million ($1.05). Revenue for the nine months rose to $1.47 billion from $1.15 billion.