Authorities lifted a three-day-old curfew today and troops and tanks were withdrawn from strategic squares as Cairo returned to normal after the city's worst riots in 25 years.

At least 79 persons were killed and at least 700 injured in clashed between riot police and citizens protesting increased prices for food and other necessities Tuesday and Wednesday, the Interior Ministry said today.

Out of nearly 1,500 persons arrested, more than 1,000 are still in custody and will stand trial, officials said.

The Soviet Union today described as "slanders" Egyptian government charges that the underground Egyptan Communist Party had organized the riots. A commentary in the Soviet Communist Party newspaper Pravda said Egypt's large balance of payments deficit, which had prompted the food price increases that triggered the riots, were caused by Egypt's economic ties with the West.

President Anwar Sadat suspended the price increases after rioters ransacked nightclubs, smashed shop windows, police stations and other establishments.

The order lifting the curfew was issued by Premier Mamdouh Salem in his capacity as deputy military governor of Coiro, the state-run Cairo radio said. The order also applied to Alexandria, Suez and other cities and towns where disturbances caused the curfew to be imposed.

Damage in the city of Cairo alone was estimated at several million dollars, a spokesman said. This includded the cost of some 100 public buses and 20 street cars that were burned or damaged by demonstrators, sources said.

Paratroopers were deployed to guard main squares, banks, bridges, government buildings and fuel stations. Six Soviet-made tanks were positioned at a square, cutting off the city from its main working-class districts where the riots were bloodiest.

Israeli Defense Minister Shimon Peres told a meeting in Tel Aviv that the Egyptian authorities "pulled their forces, particularly armored vehicles, out of Sinai to put down the riots and intimidate the demonstrators."

The price increases protested by the demonstrators were advised by the International Monetary Fund and Western economists who advocated that the Egyptian government lift its subsidies for several consumer goods in an attempt to make up part of the $3.2 billioin estimated deficit for 1977.

These other developments were reported today:

U.S. Secretary of State Cyrus Vance is expected to visit Egypt in late February as part of a Middle East exploratory tour, the leading Cairo newspaper Al Ahram reported.

Vance also is expected to visit Jordan, Syria and Israel next month, U.S. sources in Amman said.

Arab League Secretary General Mahmoud Riad and his wife suffered multiple fractures in a car accident Friday in Cairo, and Arab League official said. Their condition was described as satisfactory.