BELFAST, Northern Ireland (AP) _ A lone gunman shot to death a Roman Catholic police sergeant as he went to Mass Sunday at Enniskillen near the border with the Irish Republic, officials reported. He was the 10th police officer killed by guerrillas in four days.

A police spokeswoman said Sgt. Hugh McCormac, 40, was shot as he entered a monastery called St. Gabriel's Retreat with his wife and their 16-year-old daughter and 15-year-old son.

Witnesses said the killer opened fire with a pistol at point-blank range, then fired several more bullets into the sergeant as he lay bleeding on the ground beside his screaming family.

The gunman fled in a car driven by another man, the police spokeswoman said. Police sources said they believed the gunmen drove across the border into the Irish Republic.

There was no immediate claim of responsibility, but police blamed terrorists of the outlawed Irish Republican Army. It is fighting to drive the British out of Northern Ireland, a British province with a Protestant majority, and unite it with the predominantly Roman Catholic Irish Republic.

Meanwhile, Douglas Hurd, Britain's secretary to Northern Ireland, said Britain and Ireland were holding talks on Dublin's efforts to resolve the Northern Ireland conflict.

''We are discussing ways in which their views could be represented to us in a more methodical way than they are at present,'' Hurd said on Independent Television's ''Face the Press'' program.

Hurd said such political efforts were no substitute for a security policy to restrain terrorism, however. ''They can help deprive the IRA of support. That is very important. But it is terrorism which is the priority,'' he said.

McCormac, a training officer at the Royal Ulster Constabulary's academy in Enniskillen in County Fermanagh, was locking the door of his car as he was shot, witnesses said.

The bishop of Clogher, the Rev. Dr. Joseph Duffy, denounced the murder, which occurred in his diocese. ''The circumstances of this latest crime are especially brutal and add a dimension of desecration to the current campaign of murder,'' Duffy said.

The killing occurred as mourners buried three Royal Ulster Constabulary officers who perished in an IRA mortar attack Thursday on a border police base at Newry. Nine officers were killed in the attack.

Sunday's slaying heightened fears in Northern Ireland that Protestant extremists opposed to the overwhelmingly Catholic IRA will launch revenge attacks.

Protestant politicians are pressuring the British government to unleash an offensive against the guerrillas. The Ulster Defense Association, Northern Ireland's biggest Protestant street army, has threatened to strike at IRA hideouts in the Republic of Ireland.

Ken Maginnis, the British member of Parliament for South Fermanagh, said of the latest killing: ''I'm horrified to think that a man going to worship his God is cut down by these barbaric and godless men.''

Maginnis, a former major in the locally recruited Ulster Defense Regiment, said that Catholics ''surely must realize these IRA killers do not care whether it's a Catholic or a Protestant that they gun down.''

At least 2,430 men, women and children have been killed since sectarian strife broke out in Northern Ireland in August 1969. Of that number, 210 were members of the Royal Ulster Constabulary.