The World Bank expects to approve a loan well in excess of $100 million and possibly as much as $300 million to Iran to help finance construction following the June 21 earthquake, bank sources confirmed last night.

It will be the first World Bank loan to Iran since the mid-1970s, said bank spokesman Tim Cullen.

Representatives of the World Bank expect to spend four weeks appraising damage from the earthquake, which killed an estimated 40,000 people, Cullen said. After they report their findings, the bank's executive board is expected to meet in early December to approve the loan. The current appraisal is the third on-the-spot survey of Iranian needs since February.

The initial estimate of the earthquake damage indicated that the costs would be in the vicinity of $100 million, Cullen said. But in August, bank representatives determined that the damage was more severe than originally thought, and the costs are now calculated at about $600 million.

The bank might finance up to half of that figure, sources said. Bank officials are looking for other possible sources of help, including the Islamic Development Bank.

The World Bank's relations with Iran deteriorated during the reign of Shah Mohamed Reza Pahlavi, when it disagreed with the ruler's basic economic policy. The Shah then, in effect, severed relations with the bank. After the major boosts in oil prices in 1973 and 1979, Iran grew wealthy enough to avoid the need for borrowing from international agencies.

But in the aftermath of its devastating eight-year war with Iraq, and the subsequent drop in oil prices, Iran once again fell within the per capita gross national product that qualifies it to become a World Bank borrower.

Iran's most recent relationships with both the bank and the International Monetary Fund have been cordial. At the last IMF/Bank annual meeting here, the Iranian finance minister served as chairman of the so-called Group of 24, representing the Third World group of nations within the IMF.