Doubts cast on British security policy in N. Ireland after killing of Unionist

The murder of a leading Ulster Unionist politician by the Provisional wing of the illegal Irish Republican Army in Belfast Wednesday makes it more difficult for Britain to find a way out of the Northern Ireland morass.

The killing has intensified fears that the government's security policy against terrorism is inadequate.

And it represents a further setback to the task of finding political consensus between Protestant and Roman Catholic politicians.

The murder will harden attitudes at a time when the troubled province badly needs a period of relative calm to enable its people to reflect on the current and disastrous spiral of violence.

Edgar Graham was shot dead by gunmen as he checked in at Queens University, Belfast, where he was a lecturer in law. He had arrived on the campus to deliver a paper on ''Law in the European Community.''

Mr. Graham was the Official Unionist spokesman on home affairs. He was known for his strong stance against the segregation of Republican and loyalist prisoners at the Maze prison near Belfast.

He was also a firm supporter of the so-called ''supergrass'' system, by which a number of terrorists have been granted pardons by Northern Ireland courts in return for information that has convicted other terrorists. Graham was a rising star in Unionist circles and was tipped as a likely future leader of the party.

Significantly, there were tributes from all sides of the political divide. Seamus Mallon, deputy leader of the Social Democratic and Labour Party, which is mainly Roman Catholic, termed the killing ''a naked sectarian act against a person elected by the Unionist community. . . . It is a sectarian act of murder against that entire community.'' James Prior, the British secretary for Northern Ireland, expressed shock at the killing.

But Mr. Prior's statement was overtaken by events as furious Unionist politicians called for tougher security.

Meanwhile, the Provisional IRA claimed responsibility for the murder. A statement said: ''Today's execution of Edgar Graham should be a salutary lesson to those loyalists who stand squarely behind the laws and the forces of repression of the nationalist people.''

Allowing for the predictable Provisional IRA rhetoric, this killing is a direct attempt to further damage the prospects of finding political agreement in the Northern Ireland Assembly. Unionist political pressure on Mr. Prior to strike against Republican terrorism will increase.