A positive opinion poll is always a delight to political parties. But when the findings approach record-breaking proportions in the middle of a Dail by-election campaign, there is more to celebrate than usual. And so, last night, Fianna Fail and the Taoiseach were mightily pleased with themselves.

They had good reason for celebration. The heights of popularity scaled by Fianna Fail and Mr Ahern last April, in the immediate aftermath of the Belfast Agreement, had been invested and secured during the following six months. The Irish Times/MRBI opinion poll shows the Taoiseach's personal satisfaction rating at 81 per cent, almost 20 points clear of all other party leaders.

Fianna Fail has a support level of 56 per cent in the State. And satisfaction with the coalition Government stands at 68 per cent. It is a seriously impressive record.

Marginal slippage in support and satisfaction ratings from the historic highs of April was only to be expected. But the bottom line remains: the party had rarely been in better fettle.

Not that Fianna Fail had been particularly anxious to have its political strength exposed at this time. It might have been better to contest the Cork South Central by-election as the underdog, lulling the opposition parties into a false sense of security. But now that the truth is out, the party will go for the extra seat with pennants flying.

Fianna Fail has a good candidate. Ms Sinead Behan is an impressive, young, articulate woman who projects the kind of youthful, professional image which Mr Ahern wishes to encourage. On the figures, she will be hard to beat.

In the 1997 general election, Fianna Fail won three seats out of five in the constituency with 43 per cent of the vote. Fine Gael won two seats with 31 per cent. And the Labour Party, with 9 per cent, lost the seat held by Mr Toddy O'Sullivan.

The tragic death of Mr Hugh Coveney earlier this year caused the by-election. And Fine Gael has chosen his son, Mr Simon Coveney, to contest the seat. Mr O'Sullivan is fighting hard to return to the Dail. And Mr Peter Kelly is contesting on behalf of the PDs.

In spite of the fact that Fianna Fail support in Munster now stands at 52 per cent, nobody expects that figure to be reflected in the by-election result. By the same token, Fine Gael hopes for a massive increase in its current support level of 22 per cent, while the Labour Party, with 15 per cent, has similar ambitions.

By-elections are odd phenomena. They do not reflect what happened in general elections, even in the same constituency. And they rarely echo national sentiment. Of their nature, they are dominated by local issues, reflect the quality of the candidates, record voter sympathy and offer the electorate an opportunity to send nasty, mid-term messages to the government.

The Labour Party has won the last two by-elections against the tide of successive opinion polls. And Mr Ruairi Quinn is hoping for a hat trick. However, the received wisdom at Leinster House gives the seat to Mr Coveney on the third or fourth count. Needless to say, it is a prediction which finds no favour with either Ms Behan or Mr Ahern. With two weeks to go to polling day, Fianna Fail intends to give it a lash.

While it would be hugely satisfying - if extremely difficult - for Fianna Fail to snatch a fourth seat in Cork South Central, the party's primary focus remains on June's local elections. Winning in Cork would knock Fine Gael's long-term strategy awry and do serious damage to the leadership of Mr John Bruton. However, the local elections and their potential to produce winning Dail candidates for the subsequent general election is where Fianna Fail is concentrating its greatest effort.

If Fianna Fail is to have any chance of realising its dream of an overall Dail majority, it will have to be built on solid gains made in the local elections. Last time out, in 1990, the party received a terrible drubbing in the local elections and lost control of a swathe of county councils. This weak local election base then contributed to poor Dail results in 1992 and 1997, when the party secured less than 40 per cent of the national vote.

Mr Ahern is keenly aware that his long-term future as party leader could hinge on the local elections. And he will have been greatly heartened by the finding that the level of Fianna Fail's public support has remained at 56/ 57 per cent over the past six months. Should that finding be replicated in an election, Fianna Fail would control all the local authorities.

In the past, Fianna Fail's support in the opinion polls has fallen once an election is called. However, Mr Ahern has been writing history in recent months in terms of public popularity. And given the level of support now enjoyed by the party, it could lose substantial ground and still make significant Dail gains.

Fine Gael will be disappointed that the party has remained stuck at 20 per cent in the polls, with Mr Bruton's personal satisfaction rating declining from 56 per cent to 47 per cent. However, given the booming economy and the progress being made by the Government on Northern Ireland, it could hardly have expected anything else.

Victory for Mr Coveney in Cork South Central is regarded as the launching pad for the party's recovery programme, which is designed to feed into the local and European elections. Should that plan misfire, however, Mr Bruton and Fine Gael will be in deep trouble.

There is little joy in the poll for the Labour Party which marginally increased its support to 12 per cent, while public satisfaction with Mr Quinn dropped from 58 per cent to 51 per cent.

If Labour is unhappy, the Progressive Democrats must be devastated. In spite of sharing in the most popular government ever assessed, its support base has contracted to 2 per cent. The curse of coalition, whereby the major party garners all the kudos arising from positive developments while the smaller party declines, has bitten deeply.

And the continuing high popularity of the Tanaiste, Ms Harney, at 62 per cent, has failed to halt it.

Democratic Left is also in trouble, with the party returning a 2 per cent rating, while Mr Proinsias De Rossa's satisfaction rating declined from 50 per cent to 46 per cent.

Sinn Fein and the Green Party will be happy with their national profiles of 3 per cent, which promise gains in the local elections.

Fianna Fail is poised to make considerable electoral advances. A positive December Budget would set the scene. And some deft footwork by the Taoiseach could counteract negative vibrations from the Moriarty and Flood tribunals.

However, if the world economy crumbles, all bets are off.