Synagogues and mosques around the nation approached their SABBATHS under a heightened STATE OF ALERT. Security efforts were boosted as leaders sought to assure worshipers. "You can have many armed guards but if there is anxiety in the minds of the people, they will still stay away," said Rabbi Arthur Schneier of Park East Synagogue in New York. Abdul Rahman Raja, president of the Islamic Center of Kansas City, said: "We are concerned for our congregation because there have been verbal threats. . . . We are a minority, but we are also Americans." The Jewish Sabbath begins at sundown Friday. The Islamic Sabbath is Friday.