Rival arsonists struck two Protestant church buildings and a Catholic school Friday while a Protestant group promised to rally for weeks, if necessary, to force authorities to allow its annual parade through a hostile Catholic neighborhood.

The Orange Order, Northern Ireland's conservative Protestant brotherhood, has said it will defy a government ban on the parade's traditional route past Catholic homes along the Garvaghy Road of Portadown, 30 miles southwest of Belfast.A government-appointed Parades Commission has ordered the Orangemen to march along a predominantly Protestant road.

Anti-Orange protesters there have sat down on the road for the past three summers, forcing authorities to decide whose rights should prevail. The confrontation has triggered widespread violence each year and appears to be doing so again.

Arsonists struck 10 Catholic churches late Wednesday and early Thursday, gutting three. They also attacked the homes of two isolated Catholic families on Londonderry's predominantly Protestant east side.

Police made no arrests but blamed a Portadown-based paramilitary group, the outlawed Loyalist Volunteer Force.

In apparent retaliation, arsonists torched Altnaveigh Orange Hall late Thursday outside the predominantly Catholic town of Newry, then struck two Protestant church properties on Londonderry's overwhelmingly Catholic west side: St. Peter's Anglican Church and a children's play cabin beside the Ballyarnet Presbyterian Church. Police arrested one Catholic youth.

"You never think it's going to happen to your own church, your own building," said the Rev. Matthew Moore, pastor of St. Peter's, which had been extensively rebuilt - with the help of Catholic donations - after it was torched during 1996's Garvaghy Road-related mayhem. "We're thankful it isn't as serious this time as it might have been. It's confined to a small part of the vestry."

Also today, someone threw a gasoline bomb through a window of a Catholic primary school in the village of Garvagh, but fire failed to take hold, police said.

President Clinton, traveling in Hong Kong, expressed dismay at the two nights of arson attacks. "I feel personally horrible about what is happening to the churches," Clinton said. "In our country, we had this round of church burnings, you know, in the last few years."