This time, at long last, planners trying to fix City Hall Plaza have got it right.

Once those planners had grandiose visions of remaking the entire plaza.

But this week's groundbreaking for a community arcade on the northern edge of the plaza embodies a new and better philosophy, one marked by restraint and humility.

The community arcade is to run parallel to Cambridge Street and should be completed by the end of the year. Designed as a public gathering place and a venue for farmers' markets, street fairs and art shows, its $2.7 million cost will be paid by the city.

On its heels will follow two other projects. One, scheduled to break ground at the end of 2001, will be a large, $20 million renovation of the antiquated and bunkerlike Government Center MBTA station. The second, which won't get underway for several years, is a federally funded project that will create gardens around the JFK Federal Building.

All of these are in response to something few would dispute: the nine-acre City Hall Plaza - built in the mid-1960s as part of the massive urban renewal project that razed the West End and Scollay Square - is a mess.

City Hall is a forbidding Brutalist beehive, the anonymous federal buildings seem perpetually filthy and the plaza itself is a vast brick wasteland. Spend some time there and one can't help but wonder, ``What on earth were they thinking?''

The plaza is proof, perhaps, that the true legacy of the '60s was not sex or drugs or rock 'n' roll, but simply bad taste.

Few in city government loathe the plaza more than Thomas Menino, who, prior to becoming mayor, had suffered with it as a city councilor for 10 years. Indeed, Menino's oft-voiced wish is to tear down City Hall and begin again - an aesthetically sensible but, as the mayor eventually realized, financially wasteful whim.

If Menino couldn't have that, he still wanted to remake the plaza entirely. In his first year as mayor, he organized a much trumpeted ideas competition on its future. Shortly afterward, he created the nonprofit Trust for City Hall Plaza, to which he deeded responsibility for the area's redesign.

Yet the plans that emerged from the trust's deliberations were deeply flawed.

The most obvious flaw was the notion of building a hotel and parking garage on the plaza, effectively privatizing about one-quarter of the public space. Planners argued for the hotel by saying it would add around-the-clock life to the area. In truth, though, the rationale for the hotel was that it would pay for the rest of the plaza's rehabilitation - a cost the city said it simply could not afford.

There was a more subtle and deeper flaw in the trust's thinking as well - the hubris of believing that it knew the magic solution to fixing the entire plaza.

Indeed, the self-confidence of the trust was oddly reminiscent of the attitude of those who originally designed and built City Hall Plaza. Those designers, too, were certain they knew how to create a great public space.

In fact, no one really understands why some public spaces succeed and others do not. A host of factors - design, location, adjacent uses, economic circumstances, whether the space is active or passive - comes into play. One can easily point to examples where one public park works while a similar one fails.

The Public Garden, for example, is an enormously successful passive green oasis. Yet the nearby Boston Common, also a big, passive green space, was for years a failure until the city created active uses such as the year-round skating rink and wading pool at the Frog Pond.

Menino and the trust learned from the mistakes of the past, however. Rather than proceeding blindly forward, the trust conducted more than 100 public hearings, many in the City Council chambers.

They were not easy hearings. Criticism of the trust and its plans was often harsh. A citizens' advisory panel, appointed by Menino in response to the widespread disapproval the plans received, came in with a skeptical report as well.

It must have been tough. The members of the trust obviously thought their plans had merit. Seeing them given short shrift was undoubtedly disappointing. Yet, to their credit, they backed off and came up with a new approach. Gone now is the idea of a master plan for the entire plaza. Gone too is the notion of building a hotel and parking garage.

The community arcade is, indeed, small potatoes compared to the trust's original vision. It touches less than 5 percent of the plaza. The new arcade, combined with a new T stop and the federal gardens, should reinvigorate the northern end of the plaza. But the trust now approaches these as experiments, efforts it will learn from and, it hopes, will help guide improvements on the rest of the plaza.

People frequently profess to admire bold gestures from their civic leaders. But sometimes, as is certainly the case with City Hall Plaza, it is better to temper those gestures rather than make again the errors committed four decades ago.

Tom Keane writes every Friday for the Herald. He can be reached at tomkeane@tomkeane.com.