Twenty-five years after the United States canceled its participation in Egypt's Aswan High Dam, making way for Soviet sponsorship and touching off an international crisis, the Reagan administration yesterday announced a plan to replace dangerously worn Soviet components.

M. Peter McPherson, director of the Agency for International Development (AID), announced the decision to finance the replacement of cracked Russian-made "turbine runners" at a cost of $25 million to $50 million. McPherson said the work will be done by Allis-Chalmers, which he said is the only American firm capable of designing, testing and fabricating giant turbines of this size.

The late Egyptian president, Anwar Sadat, had initiated the plan for U.S. replacement of the cracked Soviet equipment and shortly before his death Sadat had evicted the last of the Soviet technicians at Aswan. At meetings during Sadat's funeral, his successor, Hosni Mubarak, urged Secretary of State Alexander M. Haig Jr. to take quick action on this and other aid programs for Egypt.

The Reagan administration promised to accelerate military and economic aid to Egypt to help shore up Mubarak. The relatively small and uncomplicated Aswan project is the first tangible accomplishment.

Officials said a steady and impressive flow of tanks and armored personnel carriers from the United States should begin by next summer, and new warplanes will arrive by the end of next year. Economic aid programs are reported still to be bogged down in complex administrative procedures and complicated by the failure of Congress to pass foreign assistance bills.

Close to $2.5 billion in economic aid is still moving tortuously through the bureaucracy, by official accounts.

The Aswan dam on the southern reaches of the Nile was the pet project of President Gamal Abdel Nasser, who saw it as the way to harness the annual and erratic flooding of the mighty river. Initially the United States and Great Britain, with help from the World Bank, were to finance the venture.

In July, 1956, then-Secretary of State John Foster Dulles, piqued by Nasser's neutralism, canceled American participation. Britain followed suit. Nasser, in response, turned to the Soviet Union for engineering, construction help and financing, an action which cemented Cairo-Moscow relations.

Nasser also surprised the world by taking full control of the Suez Canal and seizing the assets of the Suez Canal Co., partly to obtain the revenue to finance the dam. In the international uproar which followed, Israel, Britain and France attacked Egypt, but withdrew their forces under heavy American pressure.

Because of its history, the Aswan dam was a symbol of Egyptian-Soviet cooperation and of Western antipathy.

According to AID officials, cracks began appearing in the Russian turbine runners, which are structures holding up the turbine blades, about two years after the hydroelectric power plant at the high dam began operations in 1967. "The number and severity of the cracks have been steadily increasing, despite Egyptian efforts to correct the problem with a regular program of welding repairs," the AID announcement said.

The Aswan hydroelectric plant produces more than 50 percent of Egypt's total power supply, according to AID. Officials said a U.S. Bureau of Reclamation team sent to Aswan two months ago concluded that failure of turbine components was "imminent," with a growing risk of power losses.

It will take nearly two years from the signing of a contract before the first of the 12 turbine runners is replaced by Allis-Chalmers. The replacement of all will take six years, AID said.