Rejecting Washington's demands that Cuba embrace capitalism, Foreign Minister Felipe Perez Roque told hundreds of fellow lawmakers that consecrating socialism in the constitution could help the current system survive after Fidel Castro and his brother Raul die.

Perez Roque's unusual public reference to the mortality of both Cuba's president and his designated successor came Tuesday night, on the eve of a third day examining a constitutional change that would declare Cuba's economic, political and social systems to be "untouchable."

The National Assembly's discussion of the amendment, backed in speeches over two days by nearly 100 lawmakers, comes as Cuba feels increased pressure from at home and abroad to carry out democratic reforms.

There was some public discussion of Fidel Castro's inevitable death a year ago after he briefly fainted in the broiling sun. But Perez Roque's frank acknowledgment of the eventual deaths of both Castro brothers — and their entire generation of original revolutionaries — was rare.

The proposed constitutional amendment is "key," said Perez Roque, to "what we do when the generation that carried out the revolution, and the command of it today, the generation of Fidel, of Raul ... is no longer with us."

"The key is not to be disarmed of our ideas," said the foreign minister, who at 37 is among the youngest of the ranking officials in the communist government.

While many speakers referred to the corruption, poverty, and racial discrimination of Cuba before the 1959 revolution that brought the Castro brothers to power, Perez Roque used another country as a point of reference.

The foreign minister noted that the Soviet Union collapsed "even though 75 percent of the population had supported a referendum against dissolution just a few months before."

Fidel Castro, who will be 76 in August, and Raul Castro, the 71-year-old defense minister, presided over the gathering of nearly 600 National Assembly deputies gathered for the special session. They both are also members of parliament.

The session originally was expected to take two days, but on Tuesday evening National Assembly President Ricardo Alarcon announced that the session — and a nationwide work stoppage — would continue into Wednesday. The government has closed banks, schools and most offices and factories so citizens can follow the sessions, which are being broadcast live on state television.

The government says the proposed amendment is its answer to President Bush's refusal last month to lift American trade and travel restrictions until the Caribbean island undertakes reforms including multiparty elections.

The measure also appears to be Castro's effort to undermine the Varela Project, a homegrown effort to organize a referendum on the question of reform, said opposition activists and a Latin America specialist who traveled here with Jimmy Carter last month.

"No other country, to my knowledge, has ever tried to make any part of their constitution impossible to change," said Robert Pastor, a political science professor from Emory University.

"This may be a sign that they view Varela as a threat and are trying to pulverize it," said Pastor, who sat in on Carter's meetings with Castro and other high-ranking officials. "If so, this is a sign not of strength, but of fear."

In a telephone interview from Atlanta, Pastor said he had been a delegation adviser and could not speak for the former president's Carter Center, which has not commented on Cuba's proposed amendment.

Pastor said the delegation had extensive talks with senior officials about the Varela Project, which seeks a referendum on whether Cuba should embark on reforms such as freedom of expression and the right to own a business.

A few days before Carter arrived, organizers delivered a petition with 11,000 signatures to the National Assembly. But most Cubans had never heard about the homegrown effort until Carter mentioned it in a speech here. Six weeks later, the unicameral parliament has not responded.