Reza Fallah, an Iranian oil official under the Shah, died Dec. 5 at his home in Windsor, England, according to reports from London. He was 73 years old. Mr. Fallah was deputy chairman of the Iran’s National Oil Company from 1974 to 1979, when he followed Shah Mohammed Riza Pahlevi into exile. Earlier he managed the Abadan oil refinery after it was taken over in 1950 from the Anglo-Iranian Oil Company and put under Government control. Trained in petroleum engineering in Britain, Mr. Fallah was regarded as a key figure in the shaping of Iran’s oil policy. After the Iranian revolution, Prime Minister Mehdi Bazargan asked him to return and take over the oil industry, but Mr. Fallah declined.