Spain's new Socialist government, in its first Cabinet meeting since taking office last week, today approved the partial lifting of the Gibraltar blockade that was imposed 13 years ago by Francisco Franco in an attempt to force the return of the British colony to Spanish sovereignty.

Prime Minister Felipe Gonzalez told a press conference the blockade would be lifted for pedestrians only on Dec. 15. He said the measure had been taken for "strictly humanitarian purposes" and was not linked to any agreement between Madrid and London for an end to border restrictions or simultaneous ministerial talks on the sovereignty issue.

The unilateral Spanish move on the dispute that dates back more than 250 years is seen by British diplomats here as a prelude to a call for full talks. Planned negotiations were postponed indefinitely earlier this year at the height of Britain's war with Argentina in the Falkland Islands.

In a second foreign policy directive, Gonzalez said Foreign Minister Fernando Moran had been instructed to attend the NATO ministerial meeting on Dec. 9 in Brussels, where he would explain the Socialist government's decision to freeze negotiations aimed at Spain's integration into the alliance's military command.

Gonzalez said Spain's national interests had not been sufficiently accounted for when the Center Party, which lost in the Oct. 28 elections, led Spain into the Western alliance in the summer.

"Spain has to restudy the whole membership dossier," said Gonzalez, "with a view to protecting our interests and creating a better climate of dialogue with alliance members."

The latter was an indicator of current thinking among Socialist officials that Madrid could use NATO membership as a bargaining chip for progress on stalled negotiations to join the European Community. The new government also links NATO membership to a solution of the Gibraltar problem and to safeguards from the alliance for the Spanish enclaves of Ceuta and Melilla on the Mediterranean coast of Morocco.

Asked about the U.S.-Spanish defense agreement signed in June and still awaiting ratification by the Spanish congress, Gonzalez said the issue would await talks in Madrid with Secretary of State George P. Shultz. He is due here Dec. 15.

Socialist spokesmen have said the new government seeks to renegotiate the agreement. It governs four U.S. bases, including the important Rota naval depot at the entry to the Mediterranean. Socialist opposition to the accord centers on its linkage to Spain's NATO membership. The agreement, short of a treaty, requires no U.S. congressional action.

An indicator of tough economic times ahead came with the Cabinet approval of a 21 percent price increase for gasoline and fuel oil. Gonzalez said the outgoing Center government had refused, for electoral reasons, to order what was an overdue increase and that his government had been left with the task of legislating an unpopular measure.

The prime minister said, however, he was satisfied with the performance of the national currency following a weekend devaluation of 8 percent. He said that the firm performance of the peseta over the past two days indicated the adjustment had been "realistic and precise."

[Meanwhile, the leftist Basque separatist organization ETA announced it will continue antigovernment attacks despite the election of a Socialist premier.]