Prospects brighten for negotiations in Chile. Chile's political opposition has long demanded reform of the regime's Constitution before next year's vote. But its demands have fallen on deaf ears. Now a pro-government party has signaled its support, raising hopes the government itself may come around.

An important right-wing party that backed Gen. Augusto Pinochet's failed reelection bid now has signaled its agreement with the opposition that Chile's Constitution should be changed. The stance of the National Renovation Party, headed by General Pinochet's former Interior Minister, Sergio Onofre Jarpa, is making it harder for Pinochet to resist all suggestions of constitutional reform, as the general did immediately after his defeat in the Oct. 5 presidential plebiscite.

Slowly, the government is moving toward accepting talks on amending the 1980 document.

The 16-party opposition coalition says the Constitution must be altered in several aspects including:

Eliminating the ban on Marxist groups.

Reducing powers for the armed forces.

Allowing direct election of senators.

Proposing new ways to amend the Constitution after it takes effect in March 1990.

Leaders of the National Renovation Party (RN) recently released their proposals for constitutional reform which coincide in several areas with those of the opposition.

This similarity of demands may indicate an imminent working alliance between the RN and some of the more conservative interlocutors from the opposition, in particular the Christian Democratic Party.

Both groups say there have been no formal meetings so far, but each looks positively on the other's reform goals.

And they feel some historical affinity. ``We've been through a lot together,'' says Federico Mekias, a member of the RN's political commission, referring to his Christian Democratic rivals. ``We faced the Marxist [Salvador Allende] regime together. We're basically the same kind of people.''

Pinochet, who finally conceded in late November that he will not run in next year's open presidential vote, technically can veto proposed changes through his representative on the junta. But after his defeat, he may not be able to exercise this power indefinitely.

His erratic outbursts suggesting that the plebiscite could be declared void or comparing himself with Jesus (``The Jews had a plebiscite too, and they chose Barrabas'') suggest he is badly out of touch.

By contrast, the new interior minister, Carlos C'aceres, left the door open to most reform suggestions during an interview three Sundays ago with El Mercurio, the largest pro-government newspaper.

RN members recognize the prudence of seeking common ground on changes now, rather than take their chances with the new civilian government which may sweep into office in 1990 with a large congressional majority and open-ended mandate.

Both RN and Christian Democrat spokesmen say they favor preserving the current economic model of export-led growth but would modify it by increasing wages and putting more money into basic social services.

Meanwhile, Pinochet is moving rapidly to leave his stamp on government and the economy before leaving office in March 1990. He has proposed a torrent of new laws to privatize large state holdings in mining, shipping, utilities, insurance, and transport. He also plans to sell the state TV channel, and remove the central bank from the control of elected officials.

These and other measures, if enacted, would limit radically the incoming government's powers.

Some opposition members promise to undo these last-minute actions after the transition. ``These deals will not be honored by the new government,'' says former Mining Minister Sergio Bitar, ``and investors should be very, very clear about that!''

Economist Humberto Vega of the Roman Catholic-oriented Academy of Christian Humanism said the bank law ``enables an appointed central bank president to sabotage the economic policy of the civilian president.''

From now until year's end, the opposition will be busy choosing a consensus presidential candidate, who is likely to be Patricio Aylwin, head of the Christian Democrats and the ``no'' campaign's spokesman during the plebiscite.

Mr. Aylwin has good relations with the rest of the opposition, and his party probably can impose his candidacy with a minimum of grumbling from smaller partners.

Then comes the summer lull. Serious negotiations aren't likely to take place before March.

Once the new administration takes over, economic demands on it will be enormous. Chile's minimum wage is about $45 a month, despite steady growth for four years, booming exports, and soaring prices for copper, its chief mineral resource.

Nonetheless, most Chileans seem disposed to wait for the regime to disintegrate on its own. Turnout has been low at the three demonstrations called since the Oct. 5 vote.

Contributing to a sense of the decline and fall of the regime is a strange murder case, which is wracking the security services. Manuel Contreras Jr., son of the former secret police chief of the same name (who is wanted in the United States for the 1976 murder of exile politician Orlando Letelier), shot and killed a retired Army major and secret police operative during an argument at a party Oct. 29.

Despite powerful connections, it is unclear whether Mr. Contreras will enjoy the accustomed impunity. Pro-government papers have editorialized sharply about the incident's implications. The normally quiescent Supreme Court finally appointed a special investigator. The scandal may result in undermining one of the regime's main pillars.