JERUSALEM (AP) _ A letter bomb hidden in a Christmas card exploded today and injured two people, and at least seven other such bombs were received in Israel and at a Jewish settlement in the occupied West Bank, police said.

Seven of the letter bombs were defused safely, but police spokesman Adi Gonen said authorities believed more explosives had been mailed. Israel radio quoted untaining Christmas cards, according to a police statement. The typewritten return address on each envelope was listed as D. Nissim, Istanbul.

''It looks like one of those greeting cards that starts playing music when you open them up,'' said Liat Collins, a spokeswoman for the postal service. She said authorities were checking whether there was anything to link the bomb recipients.

Israeli radio stations broadcast appeals through the day for residents to beware of suspicious letters.

Three bombs were discovered in the West Bank settlement of Kiryat Arba on Tuesday. Today, another bomb was found in Kiryat Arba, and one bomb was found in Tel Aviv; in the Tel Aviv suburb of Ramat Gan; in Haifa; and in the town of Or Yehuda, near Ben Gurion International Airport.

In Or Yehuda, two men suffered slight hand injuries today when they touched a letter bomb and it exploded, the radio said. One of the men was hospitalized.

A security official in Kiryat Arba said a resident alerted authorities there Tuesday when she saw two cables sticking out of the envelope.

As police defused the bomb, a mailman passed by and told authorities he had delivered two identical letters to two other Kiryat Arba residents, said the official, Yaacov Gadon. Police picked up the additional envelopes and examined them in a laboratory, Gadon said.

Asked if he had any idea why the bombs were sent, Gadon said: ''We are Jews, that's enough.''

The domestic news agency Itim quoted unidentified police officials as saying it appeared the addresses were selected at random from Israeli telephone books.

Yitzhak Kaul, general director of Israel's postal service, said that after the bombs were discovered in Kiryat Arba, postal employees were placed on alert throughout the country.

''Throughout the night we prepared for better supervision and instructed our personnel, and as a result, we discovered such envelopes in Haifa, Tel Aviv and Ramat Gan,'' Kaul told Israel radio.

Kaul said the letters bore a Dec. 23 postmark. He said the last wave of letter bombs in Israel occurred in 1972.

The letter bombs arrived as the Israeli military was cracking down on riots in the occupied West Bank and Gaza Strip that have resulted in the death of at least 22 Palestinians and the arrest of hundreds of Palestinians.