As President Suharto of Indonesia ended his 30th year in office in late 1997, there might still have been time left for a dignified exit. The regime had lost its credibility; a new generation demanded its say. But Suharto clung to power - compounding Indonesia's financial distress and internal violence. Suharto claimed his seventh consecutive term in March 1998, the cities burned in April, and the president abruptly resigned in May. National income fell 15 per cent that year.

Suharto's final struggle for power had won him two extra months. But he, of course, is not the only politician who has confused his own fate with that of his country. Mobuto Sese Seko's 32nd and final year in power in Zaire was marked by rampant corruption, looting and insurrection. Mao Zedong spent the last 10 years of his 27-year reign throwing China into utter and useless upheaval. Among current long-timers, Fidel Castro struts and preens in his 40th year of power while his impoverished compatriots abandon cars for bicycles. Robert Mugabe of Zimbabwe, Daniel arap Moi of Kenya, and Saddam Hussein of Iraq enter their third decade of rule with their countries in disarray.

There must be a better way. Yes, some tyrants, such as Saddam, are prepared to butcher their citizens and even their own families to cling to power. But others survive with tacit international assent, and sometimes active encouragement.

The community of nations lacked the practical means to convince Suharto to give up his quest for a sixth term even as the country headed for the abyss. The Ibero-American nations have just honoured Castro by holding their annual conference in Havana. The world still pumps money into Zimbabwe and Kenya. Any public statement by foreign officials that Mugabe or Moi or Castro should leave would be regarded as the gravest infringement on national sovereignty.

It is time to break the spell of silence. My modest proposal is for an international standard that "Twenty Years are Enough". This norm would be inscribed in the aid agencies, the International Monetary Fund and World Bank, the United Nations, and other donor and regional groups of countries.

Any head of state, and his henchmen, would start the clock on the first day. His countrymen would be put on notice: international support for the regime ends on the 20th anniversary of power. The world community wouldn't have to judge character on a case-by-case basis, and it wouldn't spring any surprises. Twenty years would be time enough to make preparations for a peaceful and orderly departure.

Why 20 years as the international term limit? It is mainly an empirical issue. Take the list of post-second world war leaders that lasted for 20 years or more. For every Lee Kwan Yew, who brought effective leadership in Singapore into a third decade, there are at least 10 disasters. Indeed, with almost no exceptions the long-servers form a gallery of rogues, thieves and worse. Countries should almost certainly impose an even tighter standard on themselves. The US has chosen two four-year terms, and its seems to work fine. Chancellor Helmut Kohl's years in a 16-year rule of Germany are now suspected to have been rife with party corruption and secret slush funds. It is possible, however, to go too far in the other direction. After decades of misrule, many Latin American countries adopted constitutions limiting presidents to one term. One after another now spends his term squandering public funds to sway congressmen to rewrite the rules to allow for re-election.

Would an international norm actually make a difference? Perhaps Jacques Chirac of France would have thought twice about his recent embrace of the 32-year rule of President Eyadema of Togo, in the face of pervasive reports of massive human rights violations. Perhaps the struggle between Castro and the US could have been depersonalised, and resolved much more easily, if Castro's vain desire for a lifetime's hold on office had been clipped by simple international standards.

No doubt each leader approaching the 20th year would begin to plead for exigencies. These pleas would sometimes strike a responsive chord. Hosni Mubarak, now in his 19th year, has won world plaudits for supporting peace in the Middle East and economic reform at home. And yet, isn't Egypt exactly the kind of country where the very success of governance has made possible a peaceful transition to democracy, if that transition is not too long delayed?

A good plan for international term limits will require much more than the sanction of foreign aid.

Psychologists assure us that positive reinforcements work even better than negative ones. Retiring heads of state need the flattery of presidential libraries and international diplomatic assignments - in short, the glory of politics by other means. Who knows. With some creativity, we might get a flood of worthies heading for the exits.

The author is professor of economics at Harvard University Copyright Financial Times Limited 2000. All Rights Reserved.