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JERUSALEM — Israeli officials are reacting cautiously to Jordanian King Hussein's decision to name a new successor.

Hussein's eldest son Abdullah — who now replaces the King's brother, Prince Hassan, as heir to the Hashemite throne — is largely an unknown entity, particularly with regard to Israeli-Jordanian relations.

The change of succession took on particular significance Tuesday, when Hussein flew back to the United States for treatment after developing a cancer relapse.

Hussein left after a brief airport ceremony at which Abdullah was sworn in as regent in the king's absence.

Commenting on Abdullah's sudden ascent, Reserve Col. Shalom Harari, a former Arab affairs adviser at the Israeli Defense Ministry, said the 36-year-old Abdullah has little knowledge of political or economic issues.

Harari was not alone in his assessment. Abdullah, a career soldier who leads Jordan's elite Special Forces, was described this week by close associates as having little ambition outside the military.

This lack of political experience has Israeli officials closely watching the Jordanian court, Harari added.

Many Israeli sources refrained from commenting on the situation in Amman — particularly after warnings were sounded in Jordan against Israeli interference in Jordan's internal affairs.

But speaking off the record, several sources said that they were not concerned by the royal reshuffling and that Abdullah would continue his father's policies.

Coming just days after the 63-year-old Hussein returned home from six months of cancer treatment in the United States, the decision to replace Hassan as his heir was a political stunner.

Indeed, Middle East expert Ehud Ya'ari described the move as little short of a "monarchical coup d'etat."

The decision was conveyed in a royal decree issued Monday in which the king "agreed to relieve Prince Hassan of the position he has held for the past 34 years."

Hussein has long been seen as Israel's closest ally in the Arab world — a view confirmed after Israel and Jordan signed their historic peace treaty in October 1994.

Hussein was crowned king at the age of 17 in May 1953. He subsequently carried on the pro-Western policies of his grandfather, King Abdullah, who was assassinated in 1951 after trying to make peace with Israel.

The demographic makeup of Jordan changed after the 1967 Six-Day War, when the kingdom was flooded with Palestinian refugees. Some 3 million of Jordan's current population of 4.4 million are Palestinians.

Abdullah, 37, is the son of Hussein's second wife, Queen Mona.

Married to a Palestinian woman, Abdullah is seen by some sources in Jerusalem as better positioned to maintain a good relationship with Jordan's Palestinian majority.

But some in the Jewish world were saddened by the decision to bypass Hassan, who for decades was designated Hussein's successor.

While lacking the charisma of the king, Hassan, 52, is a familiar figure among Jewish audiences, who viewed him as likely to carry on his brother's policies toward Israel.

For years, the king and his brother had worked closely, with nothing in their behavior betraying any strains. When Hussein left for the United States six months ago, he entrusted Hassan with control over Jordan's affairs.

But according to reports in Jerusalem, problems developed when Hassan behaved as if Hussein was not coming back.

Shortly after Hussein left for the United States, Hassan spoke publicly of the need to eradicate corruption. Jordanians loyal to the king wondered whether the comment was meant to imply that Hussein had condoned corruption.

In a sign that relations between the two were cooling, Hassan did not visit his brother's bedside during the months Hussein spent at the Minnesota-based Mayo Clinic.

In addition, Hussein had expressed concerned that as king, Hassan would pass on the line of succession to his own sons, not the king's.

With his own mortality evidently in mind, Hussein moved quickly to dispel growing speculation about the line of succession.

Queen Noor had wanted her eldest son, Hamza, 19, to be appointed crown prince. Indeed, palace officials said Hussein was grooming Hamza for the position. Hamza was the only of Hussein's five sons to be at the monarch's bedside during the past six months.

But analysts say that Hussein ultimately decided that Jordan is facing too many problems — an economic crisis, an internal struggle for more democracy, tension with Iraq and Syria, and the Israeli-Palestinian peace process — to allow the throne to pass to a young, inexperienced leader.

"One of the main issues on the national agenda is the Hashemite concern about a Palestinian state," said Ya'ari. "Hussein is well aware of the fact that once a Palestinian state becomes a political reality, it will have a major affect on Jordan.

"Only a solid grip on the armed forces, ensuring their continued loyalty, will prevent turning the country into a de facto Palestinian state."