Although the Mexican government urgently needs cash, it has not used all the money made available to it late last month by the United States and other industrialized countries as the first part of an emergency rescue package, European sources said yesterday.

Officials are puzzled about why the Mexican government has not drawn all the money that it could, because it is extremely short of cash and reportedly has had great difficulty meeting all its immediate debt obligations.

One official speculated that this was evidence of the confusion over economic and financial policy in the last weeks of the lame-duck government of Jose Lopez Portillo, and also reflected the very slow progress in talks between the Mexicans and the International Monetary Fund over a loan that U.S. officials characterized as the "keystone" of any settlement to Mexico's financial crisis.

The second and third parts of the $1.5 billion loan package were conditional on the Mexicans making "progress toward agreement" with the International Monetary Fund on an austerity package and loan program. Negotiations virtually stalled for a time after the lame-duck Mexican government nationalized private banks and imposed strict exchange controls three weeks ago, although there is now some evidence of progress, sources said yesterday.

An IMF team has been back in Mexico for over a week, but the head of the team only flew to Mexico Thursday, an international official said yesterday. This may suggest that the groundwork has been laid for more detailed negotiations, he said.

The main participants in the central banks' loan, which was organized through the Bank for Inernational Settlements in Switzerland, will gather there this weekend in the first of their regular meetings since July. Some of the nations have said they think Mexico should be given no more money now because of the slow progress in the IMF talks, European sources said.

The new Central Bank governor, Carlos Tello, reportedly has softened his opposition to the IMF, a New York financier said.

However, bankers still fear that any agreement between Mexico and the fund will have to wait until the new government of President-elect Miguel de la Madrid takes over on Dec. 1.

Although rumors have spread that Mexico recently has failed to make some interest payments, bankers yesterday said that it is difficult to determine whether this is so. In any case, they are extremely unwilling to call a default. The 90-day grace period on repayments of government loans which banks agreed to last month will run out on Nov. 23, but so far there have not been substantive discussions on what happens after that, bankers said yesterday.