Tonight at sundown, Jews around the world begin the celebration Rosh Hashanah, the Jewish new year that ushers in high holy days.

According to the Jewish calendar, which dates to the creation of the world, tonight begins the year 5740.

Although the new year is a time of joyful celebration, Rosh Hashanah and the 10 "Days of Awe" that follow are a solemn period of introspection and repentance.

Traditionally, even those Jews who do not attend sabbath services during the rest of the year, make a point of attending services during the high holy days.

Jews believe that on Rosh Hashanah God opens the "Book of Life," which remains open for 10 days and is closed on Yom Kippur, which begins on the evening of Sept. 30.

The Jewish faithful devote this period to introspection and atonement for the previous year's sins, in hopes that they will be recorded favorably in the Book of Life.

For this reason, Jews traditionally greet each other during the holy days with messages in Hebrew such as, "May you be sealed in the Book of Life."

A Rosh Hashanah statement from the American Jewish Joint Distribution Committee reminds Jews that this "is the traditional period for reassessment and renewal of spiritual values. But spiritual values do not exist in a vacuum. Good thoughts must be accompanied by good deeds," the message continues. Reaffirmation of the faith of our fathers must be accompanied by dedication to practical works on behalf of the community."

Traditional parts of the holy days are the blowing of the shofar (a ram's horn) during services and eating apples and other fruits dipped in honey and eating challah, a sweet round bread. The sweets symbolize the beginning of a new sweet year.

Orthodox and some Conservative congregations observe Rosh Hashanah for two days, so that the correct day will be observed, even if the lunar calculations are in error. Reform congregations usually celebrate the holiday on only one day.

The Council of Jewish Single Adult Clubs of Greater Washington will hold high holy day religious services this year at Walter Johnson High School, 6400 Rock Spring Dr., Bethesda. Spiritual leader at the services will be David Golinkin, a student at Jewish Theological Seminary, New York. For further information, call 953-7100 ext. 372 or 337-0981.