HOUSE DEMOCRATS go to the table this week for what could be last game on contra aid, confident that they can beat Ronald Reagan. Unless, of course, he has an ace up his sleeve.

The only card the president showed in his State of the Union address is a Sandinista defector named Roger Miranda, who has been kicking around town for the last month.

The Democrats, think they have a winning hand this time.

For instance, they have Daniel Ortega at the Vatican meeting with the pope. In 1985, the Nicaraguan president went to Moscow at a critical moment, and the president won the next session.

In Central America, despite all the threats and warnings by national-security adviser Colin Powell and the State Department's Elliot Abrams that peace could be hazardous to their health, the five Central American presidents are holding together on the peace process. Daniel Ortega pledged to lift the state of siege in his country, hold ceasefire talks with the contras and expand press freedom.

It should be noted that in Managua, La Prensa, the paper Ortega finally allowed to re-open, showed its gratitude by printing, in 48-point type, "Sandinistas surrender."

The contras and the Sandinistas are meeting face to face in Costa Rica to arrange a ceasefire. The chief intermediary, Cardinal Obando y Bravo, a hard-line anti-Sandinista cleric whom Reagan thought he could depend on, declared that as long as progress is being made, all outside aid "should be frozen for all eternity."

The five Central American presidents, with Oscar Arias of Costa Rica as their leader, publicly urged Congress not to vote for any bill that includes military aid.

"If that happens," said Arias, who has just completed a strenuous round of knocking Latin heads together, "I would have to go back to Oslo and return the Nobel Peace Prize."

For the first time, the Democrats do not have the poisoned choice of seeming to be either for the Sandinistas or for the contras. It is differently cast this time. Either they vote to kill the Arias peace plan or they vote to end a war the contras cannot win. If they beat the Reagan program this time, they will be free of the issue forever. This is Reagan's last stand.

Except for Arias, Reagan could probably have kept the war going forever by red-baiting the Democrats. But the combination of Arias and House Speaker Jim Wright, who gave his early support to the plan and refused to wither under White House invective, has caused Reagan to pause.

He sought to show his concern for the peace plan by scaling down his originally proposed aid request from $270 million to $36 million, with only $3.6 million for military aid. The $3.6 million would be withheld for a month and could be released by the president after "consultations" with four of the five Central American presidents if there were no negotiated ceasefire by then.

Democrats balk at the idea of the president's finger on the trigger.

Says Rep. Michael Andrews (D-Tex.), "Who could possibly think the president is going to do anything but give them the aid?"

The supposedly modest request for $36 million is not all the contras would actually get, according to Rep. David Bonior (D-Mich.), chairman of the House Democratic Task Force on Nicaragua. The administration also wants a $20-million airplane-insurance fund, which means the contras could immediately buy eight or 10 planes to replace any that were shot down. In addition, there would be an unspecified amount for protective radar.

The administration says that $33 million will go for "non-lethal" aid, which they hope the dubious will mistake for "humanitarian" aid. But in the past, that "non-lethal" designation has allowed for the purchase of helicopters, trucks and fuel for planes and trucks. No one who has followed events thinks that the helicopters will be making drops consisting exclusively of medicine, bandages and food or that the trucks will never transport troops.

Last Wednesday, the White House briefly took heart. The Democrats began talking about a "package" of their own, one which the White House promptly seized on it as a sign of weakness. The Democrats do not dare risk defeat in an up-or-down vote, crowed the president's men; they have to have an alternative.

"On the contrary," says Rep. Tony Coelho, House Democratic whip, "it shows our strength. We want to close the last chapter of the Reagan war, and on the next day, introduce a plan which will be the first page of a new and -- we hope -- bipartisan approach. We will give strictly humanitarian aid to be administered by a third-party -- the church or the Red Cross or the UN High Commissioner. We will give economic help, start up trade and treat the Central Americans with the dignity and respect they deserve. It will be the end of El Patron."

Mary McGrory is a Washington Post columnist.