U.S. warplanes fired missiles and laser-guided bombs on a defense site in southern Iraq early today after it fired six to eight missiles at a British aircraft, government officials said.

The U.S. and British planes returned to their bases safely, Pentagon officials said, in what was the second American-Iraqi missile exchange in a no-fly zone since Monday.

At the White House, a senior administration official said that Iraq fired the surface-to-air missiles at the British aircraft. U.S. aircraft responded by firing two missiles and several laser-guided munitions at the Iraqi air defense station.

Iraq said an ``enemy'' plane killed a farmer and wounded two other civilians in a village. The statement, carried by the official Iraqi News Agency, made no mention of military casualties and claimed that Iraq ``almost certainly shot down a Western plane.''

A Pentagon spokesman disputed the report, saying no Western planes had been hit and that the American pilots reported striking the anti-missile site, but no village.

``We don't target farmers,'' Col. Richard Bridges said.

President Clinton was briefed by his National Security Council advisers today before flying to a South Carolina resort to begin a holiday vacation. His deputy national security team also was meeting to discuss the incidents over Iraq, the White House said.

Before leaving, the president discussed Iraq with Russian President Boris Yeltsin during a previously scheduled telephone call and agreed not to allow their differences to disrupt U.S.-Russian relations, said David Leavy, a White House spokesman.

The Russian government strongly criticized the U.S. and British bombing of Iraq in mid-December, insisting there was no justification for using force. Leavy said Yeltsin did not specifically mention the no-fly clashes that occurred Monday and today.

``Our allied aircraft will continue to enforce the no-fly zones vigorously,'' said Leavy. ``As the president has said, they are a key element of our containment policy.''

Leavy said today's incident ``underscores the continued threat that Saddam (Hussein) poses to the region. We will take the necessary precautions to carry out our mission and to protect our air crews.''

At the Pentagon, spokesman Bridges said 20 U.S. fighter jets and electronic warfare planes and four British bombers were patrolling the Iraqi skies when the incident occurred, a normal presence for a no-fly mission.

Asked if any Iraqi missiles came close to any Western aircraft, Bridges said, ``I have no indication they were anywhere near successful.'' He said the Iraqis often don't turn on targeting radar until the last second -- making it almost impossible to score a hit -- because the anti-aircraft site doesn't want to draw a radar-seeking missile response.

``I'm sure Saddam is hoping he's going to get lucky at some point,'' Bridges said. ``We have robust rules of engagement that allow us to defend ourselves adequately.''

For now, it appears that Iraq is simply taunting U.S. and British warplanes in the no-fly zone by throwing up missiles as part of a campaign to challenge the tight U.N. and American controls on the country, according to foreign policy experts.

Although Iraq, which doesn't accept the legitimacy of the no-fly zones, has claimed it is now operating aircraft in the off-limits regions, Bridges said there have been no reported sightings of Iraqi planes in the region in the past few days.

A British bomber first reported today's Iraqi missile launching at about 9:30 a.m. local time (1:30 a.m. EST) near Talil, Iraq.

``They visually detected firing. They took evasive action to avoid the missiles,'' said Maj. Joe LaMarca, a spokesman for the U.S. Central Command, responsible for American forces in the Persian Gulf, at MacDill Air Force Base in Tampa, Fla. ``I don't know for sure what they (the Iraqis) were firing at, but common sense would tell you that they were firing at the (British) aircraft.''

Two U.S. F-16 bombers patrolling the area responded and fired two anti-radar missiles and a number of precision-guided bombs onto the site at 10:15 a.m. (2:15 a.m. EST), a Pentagon spokesman said.

The aircraft safely departed the area about a half hour later.

A spokesman for the British Defense Ministry said: ``The firm response to the latest Iraqi provocation is ample evidence of our commitment'' to patrol the no-fly zone.

No activity was reported in the northern no-fly zone. Senior Airman Adam Stump, a spokesman for Operation Northern Watch said: ``We've been carrying out flights as usual today. Everyone arrived safely. There were no incidents reported.''

On Monday, U.S. warplanes exchanged missile fire with Iraqi air defenses when the planes were fired upon by Iraqi surface-to-air missiles. In Baghdad, the Iraqi military said Monday's U.S. attack killed four Iraqi soldiers and injured seven others.

Clinton described the earlier incident as a demonstration of American resolve to keep a lid on Iraqi leader Saddam Hussein's military forces, which were among the main targets of a four-day U.S.-British missile assault less than two weeks ago.