JERUSALEM — The Israeli military said Tuesday that it had agreed to allow a United Nations agency to bring building materials for 1,200 new housing units and 18 new schools into Gaza, one of the largest construction projects in the Palestinian coastal strip in years.

An Israeli military spokesman said the project came in addition to 130 others, including 14 schools, approved for construction by various agencies in Gaza.

Israel controls the cargo crossings into Gaza and has banned construction materials like concrete and steel from going in for fear that Hamas, the militant group that governs Gaza, would incorporate them into weapons and bunkers.

But after Israel’s war there in 2008-9 aimed at stopping Hamas’s rockets, and an Israeli attack on a pro-Palestinian aid flotilla a year ago that killed nine activists and led to widespread criticism of Israel’s Gaza blockade, Israelis agreed to allow construction products into Gaza if they were under the close supervision of international agencies.

With a population of 1.7 million, Gaza is in urgent need of 50,000 housing units and dozens of schools to alleviate overcrowding. Robert H. Serry, the United Nations representative to the Middle East, said Tuesday that he welcomed the Israeli approval of construction materials as a “significant step.”

Christopher Gunness, a spokesman for the United Nations Relief and Works Agency, which is building the housing and schools, said the approval came after lengthy negotiations and should be judged once the materials have entered Gaza. The housing, he said, was for refugees in southern Gaza who had lost their homes nearly a decade ago during the second Palestinian intifada.

Israel and Mr. Gunness’s agency have been bickering for months over whether requests had been made or approved and who was at fault for delays.

A new flotilla of activists protesting Israel’s policies in Gaza plans to set sail next week. Israel has offered to bring any aid cargo in by land but vowed to stop the boats from reaching Gaza.