The Bush administration has been flying surveillance drones over Iran for nearly a year to seek evidence of nuclear weapons programs and detect weaknesses in air defenses, according to three U.S. officials with detailed knowledge of the secret effort.

The small, pilotless planes, penetrating Iranian airspace from U.S. military facilities in Iraq, use radar, video, still photography and air filters designed to pick up traces of nuclear activity to gather information that is not accessible by satellites, the officials said. The aerial espionage is standard in military preparations for an eventual air attack and is also employed as a tool for intimidation.

The Iranian government, using Swiss channels in the absence of diplomatic relations with Washington, formally protested the incursions as illegal, according to Iranian, European and U.S. officials, all speaking on the condition of anonymity because of the sensitivity of the matter.

A U.S. official acknowledged that drones were being used but said the Iranian complaint focused on aircraft overflights by the Pentagon. The United States, the official said, replied with a denial that manned U.S. aircraft had crossed Iran's borders. The drones were first spotted by dozens of Iranian civilians and set off a national newspaper frenzy in late December over whether the country was being visited by UFOs.

The surveillance has been conducted as the Bush administration sharpens its anti-Iran rhetoric and the U.S. intelligence community searches for information to support President Bush's assertion that Tehran is trying to build nuclear weapons.

The Washington Post reported Saturday that the intelligence community is conducting a broad review of its Iran assessments, including a new look at information about the country's nuclear program, according to administration officials and congressional sources. A similar review, called a National Intelligence Estimate, formed an important part of the administration's case for war against Iraq.

Bush's senior advisers, including Secretary of State Condoleezza Rice and Defense Secretary Donald H. Rumsfeld, said last week that a U.S. attack on Iran is not imminent but that the option remains available.

In late December, Iranians living along the Caspian Sea and on the Iraq border began reporting sightings of red flashes in the sky, streaks of green and blue, and low, racing lights that disappeared moments after being spotted. The Iranian space agency was called in to investigate, astronomy experts were consulted, and an agreement was quickly signed with Russian officials eager to learn more about the phenomena.

But the mystery was laid to rest by Iranian air force commanders, some of whom were trained more than 25 years ago in the United States and are familiar with U.S. tactics. They identified the drones early last month, a senior Iranian official said, and Iran's National Security Council decided not to engage the pilotless aircraft.

That action is considered a major policy decision and reflects Iran's belief that an attack is unlikely anytime soon.

The U.S. National Security Agency, which conducts and manages overseas eavesdropping operations, said it has no information to provide on the reconnaissance missions over Iran.

The drones are among several tools being used to gather information on Iran's nuclear programs and its military capabilities, U.S. officials said. The United States believes Iran is using its nuclear energy program to conceal an effort to manufacture nuclear weapons, but no one has found definitive evidence to substantiate that.

Iran is engaged in diplomacy with France, Britain and Germany aimed at ending a 2 1/2-year crisis over Tehran's nuclear ambitions that began when Iranian defectors exposed a large uranium enrichment facility in August 2002. Inspectors from the International Atomic Energy Agency (IAEA) have been in and out of the country since then investigating nuclear facilities.

U.S. officials confirmed that the drones were deployed along Iran's northern and western borders, first in April 2004, and again in December and January. A former U.S. official with direct knowledge of earlier phases of the operation said the U.S. intelligence community began using Iraq as a base to spy on Iran shortly after taking Baghdad in early April 2003. Drones have been flown over Iran since then, the former official said, but the missions became more frequent last year.

The spring 2004 flyovers led Iran's military to step up its defenses around nuclear facilities in the southern cities of Isfahan and Bushehr, where locals first reported the UFO sighting. Defenses were added around those sites and others last month, Iranian officials said, after it became clear they were being observed by the drones.

A Dec. 25 article in the Etemaad newspaper, translated from Farsi by the CIA, reported on "the presence of unidentified flying objects in the Bushehr sky on a number of occasions, particularly in recent weeks." After Moscow experts were called in, the Russian daily Pravda reported on "UFO mania" sweeping Iran.

One U.S. intelligence official said different types of drones with varying capabilities have been deployed over Iran. Some fly several hundred feet above the earth, getting a closer view of ground activities than satellites, and are equipped with air filter technology that captures particles and delivers them back to base for analysis. Any presence of plutonium, uranium or tritium could indicate nuclear work in the area where the samples were collected.

The last drone sightings were in mid-January, about the same time that Iran's National Security Council met in Tehran to discuss them, according to an Iranian official.

"It was clear to our air force that the entire intention here was to get us to turn on our radar," the official said.

That tactic, designed to contribute information to what the military calls an "enemy order of battle," was used by the U.S. military in the Korean and Vietnam wars, against the Soviets and the Chinese, and in both Iraq wars.

"By coaxing the Iranians to turn on their radar, we can learn all about their defense systems, including the frequencies they are operating on, the range of their radar and, of course, where their weaknesses lie," said Thomas Keaney, a retired U.S. Air Force colonel and executive director of the Foreign Policy Institute at Johns Hopkins University.

But it did not work. "The United States must have forgotten that they trained half our guys," the Iranian official said. After a briefing by their air force three weeks ago, Iran's national security officials ordered their forces not to turn on the radar or come into contact with the drones in any way.

"Our decision was: Don't engage," the Iranian official said. Leaving the radar off deprives U.S. forces of vital information about the country's air defense system, but it also makes it harder for Iran to tell if an attack is underway.

The Iranian government lodged a formal protest through the Swiss Embassy in Tehran, which passed it on to the State Department, a Bush administration official said. The complaint was then forwarded to the Pentagon and to senior Bush administration officials, the official said.

Asked last Sunday about Iran, Rumsfeld told ABC's "This Week" that he had no knowledge of U.S. military activities in Iran. Rice, who helped plan the Iraq war, said during her European trip last week that an assault on Iran was not on the agenda "at this time."

So far, the drones have added little information to Iran's nuclear file, according to U.S. intelligence officials familiar with the mission.

Estimates vary on when Tehran could build a nuclear weapon using material from its energy program. Iran has agreed to stop enriching uranium, a key ingredient for a bomb, while it is engaged in talks with European governments. Mohamed ElBaradei, the director general of the IAEA, said if Iran resumes that work, it could have enough highly enriched uranium for a bomb within two years and could complete a weapon within three years.

Iranian officials have said repeatedly that their country has no intention of building nuclear weapons.

Staff writer Glenn Kessler contributed to this report.

Commentary:
Invading another countries air space is an act of war. When Iraq invaded Kuwait we went to war to stop them. Who will stop the war mongers in the Bush White House?