EVEN loyal supporters of the Holyrood project - such as this newspaper - must be appalled at the latest jump in its cost. Watching the ''final'' estimated price, the latest in a long line of ''final'' estimates, rise by 10% to (pounds) 375m in the space of four months beggars belief, especially since there is every likelihood of worse to come. For more than five years the Scottish people have watched their new parliament rising in Edinburgh with a mixture of hope, pride, and some understandable anxiety at the cost of it all. We want a wonderful building as the focus for a better, more autonomous

Scotland, where, as the first minister said this week, any mistakes will be our mistakes. We want to take pride in what should become an architectural triumph of world renown, a valuable addition to the beauty of Edinburgh, and a fitting adornment for an ancient capital.

Yet, even we have to baulk now at the seemingly uncontrollable cost which has rightly

infuriated and embarrassed our MSPs and is outraging public opinion. Much more seriously, this unedifying saga has now reached the stage where the whole devolution project is in danger of being discredited - and that is a price too high. What to do about this sad affair is another matter. No simple solution exists, or it would have been found by now. It is all very well for some politicians, like David McLetchie yesterday, to argue the cost could have been capped two years ago, and for John Swinney to say it must be capped now. The cost was beyond capping from the moment the first piledriver broke the soil of the Holyrood site. Soon, it became obvious the

site was unacceptably small and that more expense was required for more space. Events such as September 11 ensured many millions in new funding were needed for blast-proofing of the structure. If MSPs could simply say, as Mr McLetchie does, that ''enough is enough'', then they would refuse point blank to stump up. What would happen then? Would we be left with an unworthy addition to Edinburgh's ''pride and prejudice'', that sad folly on Calton Hill? If only the issue were so straightforward.

MSPs won't receive much public sympathy for their awful quandary, and yet they are not the original culprits. They are responsible now, of course, but not solely to blame. For the root cause we have to go back to the day the Holyrood site was chosen by Donald Dewar and his advisers; before home rule but after publication of the devolution white paper in which the Westminster government, incredibly, priced the coming Scottish Parliament at between (pounds) 10m and (pounds) 40m, or the cost of opening a supermarket. If there is a scandal, then that, surely, must be it. To underestimate the cost by some millions is careless, to do so by a factor approaching 1000% is almost criminally irresponsible.

So, let's be clear: the government in Westminster cancelled the site on Calton Hill, chose the architect, selected the new site at Holyrood, settled on the main contractors, and ordered work to be started. Only much later did the Scottish Parliament inherit control, for want of a better word. This begs obvious questions: what can MSPs do about this mess, what powers do they enjoy, or lack, or need? For answers we must wait, apparently, until next week when a statement is expected from Holyrood's corporate body. All we know so far is that, in the gloomy phrase of David Black, one of the parliament project's leading critics, this was a project ''almost designed to go wrong'' - in other words the rules, or lack of them, appear to have handed the construction and design managers a dripping roast. Those demanding more millions will have a lot of explaining to do before public opinion can be convinced

that these absurd sums can be justified. Whether the money can be refused will be for our MSPs to decide, but since they did not draw up the ground rules they might well find contract law against them. Public works contracts of this kind are notorious for going wrong. Examples are easy to find, from Portcullis House at Westminster, to the European Parliament in Brussels, which cost Belgium more than (pounds) 1bn, to the London Dome, to countless roads projects, and, most spectacularly, defence contracts. None of this justifies the financial mess of Holyrood, of course, but the point is worth making that Scotland is not uniquely responsible for the occasional budgetary calamity.

There are other factors at work: under the devolution settlement it is likely the Scottish Parliament must pay for the new building, regardless of its eventual cost, within four years. Pressure on the budget will thus be increased unfairly. Would it not be appropriate now for Westminster to reconsider its sorry role in this saga and make a contribution? Before he stepped down as presiding officer, Sir David Steel was fond of saying no-one nowadays worries about the fabulous cost of the Palace of Westminster, despite questions being asked at the time about the wisdom of spending so much on a tower with a clock. In Edinburgh today the danger is that disquiet about the cost really will obscure the efficacy of home rule. Indignant taxpayers in revolt will not pause to reflect philosophically on the long-term advantages of constitutional advance: in other words, this sorry episode is in danger

of spiralling out of control and wounding Scotland's progress, just when home rule should be proving its worth.

The first minister's promised inquiry might throw light on what has gone wrong, but it probably won't resolve much. The first priority for our MSPs at their meeting next week must be to review their powers, and, if necessary, face down the contractors and challenge their ever-increasing raids on the public purse. Above all, Scotland needs to be assured the Scottish Parliament is not being regarded as a blank cheque for a greedy construction industry, and that the troubled Holyrood project will yet prove a national triumph.