Now that a new Central American peace plan is supposed to be going into effect in Nicaragua, Secretary of State James A. Baker III said this week that the United States would consider resuming economic aid to the Sandinista government.

The aid would be part of a carrot-and-stick approach to encourage the leftist Sandinistas to begin democratizing their society and to end their support of leftist rebels in neighboring El Salvador.But news coming out of Nicaragua this week indicates that the Sandinistas are up to their old tricks and that any talk of economic aid is coming way too soon.

Contra officials said the Sandinistas have moved into a region where the U.S.-backed rebels once had their strongest support and have begun a program of executing civilian supporters of the Contras. The death toll has reached about 50 in the past two months.

"They are taking advantage of the truce and peace agreements to eliminate our supporters," a Contra leader says. Those claims cannot be dismissed as propaganda since Americas Watch, a human rights group that has been critical of the Contras, has backed up the report.

In addition, the Sandinistas apparently are thumbing their noses at the agreement about the electoral council, which will oversee planned national elections next month.

Under the agreement, the Sandinistas were supposed to appoint three members and the opposition two members to the council. But Contras say President Daniel Ortega and the Sandinista-dominated national assembly are planning to appoint all five members of the council.

If that turns out to be the case, Ortega and the Sandinistas will probably get away with it. Some segments of Congress will be briefly outraged, but in the end, economic aid will probably go to Nicaragua.

The unhappy truth is, the administration and Congress - despite this week's non-military aid package to the Contras - have largely written off the Contras and are ready to deal with the Sandinistas, even if the regime doesn't keep its promises. But let's not compound this folly by throwing money at the Sandinistas.