THE public judges its police force above all else on how well it performs in murder investigations.

The public expects a great deal of the Garda: smooth traffic flow, faster response times to alarms, recovery of stolen property, keeping muggers off the streets. But nothing focuses attention on the force more than a murder.

No wonder, then, that after a spate of unsolved murders a debate still rages in the force about how it goes about these investigations. Garda middle managers - sergeants and inspectors - have called for the "Murder Squad" of the 1980s to be re formed in the hope of better results. But the Government and senior Garda management have rejected the call, and say the procedures currently being followed are best.

A murder investigation has a number of phases. The initial response is important: if a killer is known and on the loose, a cordon is thrown around the murder scene and anywhere he might have taken refuge is quickly searched.

But the typical planned "gangland" killings of recent months offer little chance of the killer being caught quickly, and in such cases where there are no immediate leads a more painstaking investigation is set in train.

First, any witnesses of the actual shooting are interviewed, and the murder scene is sealed for forensic examination. Then large numbers of gardai start house to house inquiries. In a heavily populated area - such as the wide tracts of housing estates across west Dublin - as many as 100 gardai could be ringing bells for the first day or two after the murder.

The information gathered is collated in an effort to retrospectively "freeze" the moment of the murder. After comparison of questionnaires it becomes possible to determine which cars or people seen in the area at the time are unaccounted for.

Meanwhile, detectives gather evidence on particular suspects, establishing where they were at the time of the crime and whether they had any links with the victim.

"Gathering intelligence" before moving against a suspect is now the focus of murder investigation. Previously there was what some gardai called a "rush to arrest", when shortly after the crime any plausible suspect was brought to a Garda station and interrogated. When about 80 per cent of crimes are solved as a result of interrogation, the attractions of such an approach are obvious.

BUT unlike the culprit in a crime of passion or an accidental killing, the professional criminal has proved almost impossible to crack under questioning, and is not remotely upset by a detective saying: "We know you did it".

Superintendents are trained in running major investigations and have primacy in their areas. They can call on help from Garda Headquarters if they feel it is needed.

Expert gardai are deployed as each phase of the investigation progresses. Technical staff handle the forensic work at the scene. Among other personnel, some are thought best used for gathering intelligence; others are brought in only for searches or surveillance.

Some have proved better at getting information when questioning suspects than others, and are used only for that purpose. At a later stage a separate team may take over the preparation of the book of evidence for a court.

An investigation unit which became known as the "Murder Squad" was attached to the technical bureau at Garda Headquarters until 1988, when it was broken up. Part of the reason was the history of "heavy gang" allegations and fear of promoting elitism. More efficient use of resources is also cited.

"You could have 40 or 50 men sitting around in headquarters - and no murders, and what use are they?" a senior garda asks. "And then someone would say, maybe we should be sending them out on burglaries.

So the squad was dispersed. Each Garda division is now said to have the expertise necessary for major investigations, including murders.

"It would be wrong to believe that you can only get `expertise' from Dublin," the Garda Deputy Commissioner, Mr Pat Byrne, told the annual conference of Garda sergeants and inspectors earlier this month. "Not true! It permeates the organisation."

But a large Serious Crime Unit remains based in Dublin - by far the busiest area for murders - from which staff travel to other divisions when needed.

Gardai who advocate the establishment of a new Murder Squad say the advantage lies in training and experience. In a rural division a detective might be involved in only one murder investigation a year. No matter how well trained he or she is, that offers little opportunity to build up expertise, to quickly form a view at a murder scene about what happened and who might be responsible.

Other gardai argue that a Murder Squad would prove a better use of resources because, when a murder occurs in a division, all available personnel are directed to investigating it, and other crime inquiries have to be temporarily dropped.

However, for now, Garda management is set on the "decentralised" approach, and the Government agrees.