Separatists Pose Threat to Security : Terrorism: Basques may launch attack to humiliate Spain, experts say. But little danger is foreseen from Arab extremists.

Basque separatists who may try to embarrass the Spanish government pose the greatest security threat to today’s U.S.-Soviet summit and the Middle East peace conference that opens Wednesday, anti-terrorist specialists said Monday.

The separatists, known as ETA for the group’s initials in Basque, are adept car bombers: They exploded three devices in suburban Madrid in mid-October, killing an army lieutenant and wounding five other persons, including a schoolgirl who lost both her legs.

Although ETA has no position in the Middle East controversies, it could seek to humiliate host Spain by capturing headlines while international attention is focused on Madrid, the specialists say.

Security planners discount the chances of a direct ETA attack against the peace conference or its participants in central Madrid, where officials have taken counterterrorism measures of unprecedented proportions. But they say that the use of a bomb against a Spanish target on the outskirts of Madrid is a possibility.

By contrast, little threat is foreseen from Arab terrorists who have killed in Spain before, or from a handful of far-left Spanish terrorists who call themselves GRAPO (the October First Anti-Fascist Resistance Groups).

Arab killers have not struck recently in Spain, and GRAPO, which bombed new high-speed railway tracks between Madrid and Barcelona this month, usually does not target people.

As Arab and Israeli delegations began arriving Monday, Spain wrapped its capital tight in a security web called Operation Pax.

An army of 10,000 Spanish police from half a dozen agencies ringed hotels and flanked a motorcade route from the airport with precautions ranging from chilled traffic officers to squat armored personnel carriers to big horses.

Dogs trained to detect explosives sniffed the vanguard of 4,000 journalists arriving at a press center, thronged by more carpenters and electricians than reporters.

On a raw, misty day when hopes for peace were garbed in clothes of war, Spanish marksmen patrolled rooftops around the American and Soviet embassy compounds in this high-rise capital.

An American tent went up to shelter the entrance to the Soviet Embassy, where President Bush will hold a luncheon summit this morning with Soviet President Mikhail S. Gorbachev.

Gorbachev arrived from Moscow with a rookie security team, leading observers to conclude that most of the former Soviet regulars, including three KGB generals, wound up on the wrong side of August’s abortive coup.

As conference hosts, the Americans and the Soviets have the biggest stake and the biggest security operations. Bush’s and Gorbachev’s armored limousines were flown in for the occasion.

All the other conference participants, including the Palestinians and especially the Israelis, also brought their own security teams.

The Spanish have tried to keep the Arabs and Jews separate but equal. Delegations were assigned hotels of comparable quality with the same degree of external security. They are entitled to not more than six cars in a motorcade. (Gorbachev and Bush can have as many as they like.)

Coordinating the various national security operations requires what one planner called “a simultaneous game of chess, diplomacy and bluff.”

The Spaniards, for instance, favor high-speed motorcades. The Soviets and the Americans do not; they note that on a recent visit here, the motorcade of the president of Peru was involved in a serious accident.

Just avoiding conflict between the three police agencies with jurisdiction in Madrid has been a challenge. The Guardia Civil, the national police and the Madrid police all have particular responsibilities that they are loath to surrender.

By tradition, the civil guard and the national police share responsibility for the safety of the American Embassy compound, diplomats say. One force guards the front, one the back. The dividing line between their jurisdiction has long been a particular bush beside the compound.

A similar confusion of jurisdiction at Madrid’s Barajas Airport complicated arrival plans and security for Gorbachev on Monday evening and for Bush’s scheduled arrival on Air Force One this morning.

Despite the inevitable confusion and frictions, the Spanish government says Madrid is ready. Vice President Narcis Serra, who is coordinating the government effort, told Spanish reporters that security “is guaranteed.”

And ETA is watching.

The group, whose name means Basque Homeland and Freedom, seeks independence for the mountainous Basque region that extends into France. Its members have killed almost 700 people since 1968.

Over the last year, the group has favored car bombs, although two police officers were slain by hooded gunmen as they ate dinner last week in the Basque city of San Sebastian. Last Friday, a Basque separatist was killed and another injured when a bomb they were handling exploded in the northern city of Bilbao.

On Oct. 17, a bomb in the Madrid suburbs killed Lt. Francisco Carballan and injured his 8-year-old daughter when he started his car to take her to school. In a second attack an hour later and 200 yards away, Maria Gonzalez, 40, lost her right leg, and her daughter Irene, 13, lost both of hers.

In a third ETA bomb attack in Madrid that day--the day before Spain was announced as the peace conference site--Col. Rafael Villalobos, 50, lost both legs in a car blast that badly injured his sister, Maria Antonia.

ETA, whose political arm is the third-largest party in the Basque region, wants recognition and negotiations with the Spanish government.

The government of Prime Minister Felipe Gonzalez, which must guarantee security not only for the conference but also for the Olympics next year in Barcelona and a World’s Fair in Seville, says it will not negotiate with terrorists.