U.S. specialists operating from small craft removed 10 to 12 mines they think were laid by Iran near Kuwaiti ports, and the Pentagon plans to send minesweeping helicopters to Kuwait to deal with any further threat, Reagan administration sources said yesterday.

The mines "were Russian-made and are believed to have been procured from North Korea," said a Pentagon source who spoke on condition of anonymity. North Korea has been the leading supplier of arms to Iran since the start of the Iran-Iraq war nearly seven years ago..

A State Department official, also requesting anonymity, said the mines were laid in the approaches to Kuwait's main port of Al-Ahmadi "relatively recently. And the indications were that they had been placed there by Iran."

The mines were moored with weights to the sea bottom and were designed to float just beneath the surface and explode when struck, the Pentagon source said.

They were removed by an 18-member Explosive Ordnance Disposal team, operating from small craft, the defense source said. The craft are not counted among the six U.S. ships now operating in the gulf.

The Pentagon plans to supplement the team with MH-53D helicopters capable of removing mines, defense sources said. They declined to say when the helicopters might leave. The mines were apparently dropped into the water from small boats, possibly fishing craft operating in the area, the sources said.

Last week, Pentagon officials said they were not sure whether mines found in the harbor approaches had drifted from other parts of the gulf or had been planted there by Iran.

Field reports reaching Washington this week, however, said "the mines had not drifted there," the officials said.

President Reagan announced Tuesday he was overriding congressional opposition and going ahead with his plans to place 11 Kuwaiti tankers under the American flag and provide them with U.S. naval escorts in and out of the gulf.

Kuwait, although officially neutral in the Iran-Iraq war, has been giving Iraq money and allowing goods to be unloaded at Kuwaiti ports and transported to Iraq.