LONDON (AP) _ A man Britain calls one of the Irish Republican Army's most proficient bombers and gunmen was convicted Wednesday of killing two civilians and a police bomb disposal expert in a 1981 guerrilla bomb blitz of London.

The jury of six men and six women at at London's Old Bailey criminal court delivered its verdict on Paul Kavanagh, 29, after 21/2 days of deliberation. He will be sentenced later.

The jury members did not return a unanimous verdict on Roy Quigley, 29, also a defendant in the case. The judge, Sir Anthony McCowan, sent them back to their London hotel for the night.

Kavanagh, from Belfast, was convicted of murdering widow Norah Field, 59, and Irish-born John Breslin, 18, with a bomb packed with six-inch nails that exploded outside an army barracks in London's Chelsea district Oct. 10, 1981. The bomb, hidden in a laundry truck and exploded by remote control, wounded several soldiers in a passing bus.

Kavanagh also was convicted of planting a bomb in an Oxford Street fast food restaurant that killed policeman Kenneth Howarth when he was trying to defuse it, of bombing Debenham's department store and of a bomb attack on the home of the attorney general, Sir Michael Havers.

He was cleared of the attempted bomb murder of Sir Steuart Pringle, then commandant of the Royal Marines. The general lost a leg when a bomb exploded under his car.

Kavanagh sat impassively as the verdicts were read. The only words he uttered at the trial were ''Not guilty.''

He was arrested in 1983 after police agents shadowed him to two secret caches of guns, ammunition and 112 pounds of explosives in Oxfordshire, west of London, and Nottinghamshire, north of the capital.

The jury also found him guilty of possessing explosives and guns. Police said his fingerprints and Quigley's were found on the weapons, which prosecutor Roy Amlot were to be used for ''a prolonged and deadly campaign of violence.''

Amlot said the cache included equipment for making radio-controlled and long-delay bombs with anti-handling devices that would make them explode when bomb-disposal men if they tried to defuse them.

Police believe the seizures foiled IRA plans to mount a new bombing offensive on the mainland.

The overwhelmingly Roman Catholic IRA is fighting to drive the British out of Protestant-dominated Northern Ireland and unite it with the Irish Republic.

Intelligence officers named Kavanagh as a specialist bomber and sniper used by the IRA for ''international missions.'' They said he often operated in Western Europe, organizing gunrunning missions and attacks on British army bases in West Germany.