Spanish officials have asked for a security clampdown in Washington next month when Prime Minister Adolfo Suarez visits President Carter. They fear that a commando squad sent by the Basque separatist organization ETA could launch an assassination attempt during the trip.

The request, reported today by Spain's official news agency EFE, came as five hooded gunment armed with automatic weapons killed two Spanish military men, a colonel and a major, in the downtown area of the Basque city of Bilbao.

The murders, which bring to 13 the number of senior officers killed in Spain in the last two years and to 100 the number of those who have died in acts of political violence in 1979, sent fresh shock waves through the deeply conservative military establishment.

The news agency EFE said that Spanish security agents have passed on to U.S. authorities the names, biograhies and photographs of 19 suspected ETA members who they believe are involved in the plot to assassinate Suarez. The ETA squad, according to this report, is thought by Spanish intelligence to be in Caracas, Venezuela, where there is a large Basque community.

Spanish officials, the report said, also alerted Nicaragua, Costa Rica, and Panama, which Suarez will visit before arriving in Washington on Oct. 3.

In Bilbao, Col. Aurelio Perez-Zamora and Maj. Julian Ezquerro were shot early today shortly after they left their barracks. Gunmen ambushed them at a downtown intersection and escaped in rush-hour traffic.

Sources close to the government said today's killings could signal the start of an ETA terror campaign aimed to sabotage a referendum on limited home rule on Oct. 25. A report prepared by Spanish intelligence and leaked to the press last month warned that ETA was preparing an offensive, code-named Operation September this fall against officers, troops and military depots.

The Basque separatists, who want to set up an independent Marxist state, have condemned the referendum as a sell-out to the Madrid government.

The home-rule package was negotiated by the Spanish government and moderate Basque Nationalist Party, which has the support of the majority of voters in the area. It grants sweeping powers of self-government to the Basque provinces, but it respects the basic principle of the unity of Spain.