Jews across the city today will head to synagogue to mark the beginning of their new year and holiday season.

Sundown yesterday marked the start of Rosh Hashana, the two-day Jewish New Year that begins the period of repentance for Jews leading up to Yom Kippur, the solemn Day of Atonement.

Jews have a lot to think about as they begin the year 5766, the spiritual leader of East Side Synagogue and the president of the American Jewish Heritage Organization, Rabbi Perry Berkowitz, said.

“I think it’s a time of both uncertainty and hope – a mixed sense,” Rabbi Berkowitz said. “Jews have a full plate of concern that they have to deal with.”

Rabbi Berkowitz said that in addition to concerns within the faith, “there is a feeling of rising uncertainty” among many Jews about global issues such as terrorism and the war in Iraq.

Chief among those concerns is Israel, which in the past year has withdrawn from its settlements in the Gaza Strip after 38 years. Israeli residents and troops have left even as violence has continued in the region.

The challenges Jews and their leaders face this year extend to issues both internal and external to their community, Rabbi Berkowitz said, from rising anti-Semitism abroad to the loosening of ties with their religious roots at home.

“Internally, the Jewish community is struggling with its vitality,” the rabbi said, adding that although most Jews feel a strong ethnic connection, many “don’t necessarily commit themselves to a spiritual path.”

Internationally, Jews are grappling with a rise in incidents of anti-Semitism in recent years, particularly in Europe. “That is a dark presence that hovers over Jews all the time,” Rabbi Berkowitz said.

The increases in anti-Semitism and ongoing fears of terrorism have forced some synagogues to boost security measures. The police presence on the streets will be bolstered during the High Holy Days with added uniformed and plain-clothes officers, a department spokesman said.

Despite the concerns that linger on the minds of many Jews, Rabbi Berkowitz said Rosh Hashana is a joyous holiday and that Jews have hope for the future.

“Facing all of these challenges, the American Jewish community will, like their ancestors across the centuries, turn to the deep reservoirs of spiritual faith and meaning that will sustain and strengthen them in the days ahead,” he said.