Seven convicted Provisional Irish Republican Army terrorists began a hunger strike in the Maze prison in British-ruled Northern Ireland today in an escalation of the campaign by several hundred IRA inmates to be treated as political prisoners rather than criminal convicts.

The seven prisoners, convicted of committing terrorist murders and armed robberies, are among about 400 IRA prisoners in the prison outside Belfast who refuse all cooperation with prison authorities, wear blankets rather than prison clothes and smear their cells with excrement rather than use toilets.

The Provisional IRA's decision to begin a hunger strike with these seven volunteers indicates the failure of what the IRA calls the "dirty protest" to win concessions from the British government or increased support for the IRA from Irish Catholics in Ulster, the Republic of Ireland or the United States. Although the British government offered last week to permit all convicts in Ulster to wear government-supplied civilian clothes rather than prison uniforms, it has refused to meet any other IRA demands.

But British officials are concerned about the prospect of protesting prisoners risking death from starvation during a period of otherwise relaxed tensions and renewed efforts to achieve a political solution to sectarian strife in Northern Ireland.

So far this year, there have been only half as many terrorist bombings and killings in Ulster as last year. The number of British soldiers patrolling with the Royal Ulster Constabulary has been reduced three times this year. This leaves just under 12,000 British troops in the province, compared with a peak of 21,000 at the height of the violence in 1972 and normal British Home Guard garrison strength there of 7,000 to 8,000.

Terrorist violence has been noticeably reduced in Ulster cities and towns, including Belfast.

While the constabulary takes over more of the policing in the cities and towns of Ulster, Ireland's police and Army have significantly stepped up antiterrorist patrols on their side of the meandering border between Ulster and Ireland, where the terrorists are now concentrating their hit-and-run attacks on the security forces and their sympathizers.

A $240-million antiterrorist drive announced by Ireland earlier this year includes more Irish police officers and troops on border duty, specially trained helicopter-borne commando squad, more sophisticated intelligence gathering and increased cooperation with British security forces in Ulster on intelligence evaluation and cross-border pursuit of terrorists. There has been a significant increase in the amount of explosives, arms and ammunition seized and suspected terrorists arrested by republic authorities along the border.

One reason for this increased Irish emphasis on border security has been the growing number of bank robberies and police killings attributed to IRA terrorists inside Ireland itself. Another reason is the desire by Irish Prime Minister Charles haughey to cooperate more closely with British Prime Minister Margaret Thatcher on a wide range of mutual problems, including the political future of Northern Ireland. r

Earlier this year, Thatcher and Haughey held the first of an intended series of summit meetings like those Thatcher has every six months with her counterparts in France and West Germany. At the next Thatcher-Haughey summit in December, the Irish prime minister will propose formalizing these meetings and existing contacts among Irish and British officials into regularly scheduled conferences to coordinate policies on energy, industrial development, the European Common Market, tourism and other subjects.

Irish officials envision the kind of close cooperation carried on between France and West Germany. Haughey also would like to use this framework of regular talks as a forum for Irish-British consultations on the future of Northern Ireland.

But Thatcher's government remains determined for now to try to negotiate with political leaders in Ulster a form of provincial government under British rule in which the Protestant majority and Catholic minority would share power.