About 500 inmates in two prisons returned their meals in what was intended to be a one-day protest, said Sivan Weizman, a spokeswoman for the Israel Prison Service. She added that the four longer-term hunger strikers were in satisfactory condition, and that none were now hospitalized. Three are in a prison clinic.

But Palestinian representatives of the prisoners and international organizations have expressed growing concern over the deteriorating health of the hunger strikers, who are protesting the terms of their detention. One of them, Samer Issawi, has refused food, existing on water and nonfood supplements, for much of the past 200 days, according to groups following his case. Two others who were detained in November are said to be refusing medical treatment or the provision of supplements like vitamins and minerals.

Qadura Fares, the president of the Palestinian Prisoners Society, based in Ramallah, said he had received reports that all four were in serious condition and that their lives were in danger.

The envoy of the so-called quartet of Middle East peacemakers, former Prime Minister Tony Blair of Britain, issued a statement on Friday calling on Israel to respect the rights of all prisoners in accordance with international standards, adding, “This issue needs to be resolved quickly in order to avoid a tragic outcome which has the potential to destabilize the situation on the ground.” The quartet is made up of the United States, the European Union, Russia and the United Nations.

About 4,500 Palestinians are being detained in Israel, about half of them convicted of planning or carrying out attacks against Israelis. The prisoner issue is an emotional one in Palestinian society that touches many families. Last year, hundreds of Palestinian prisoners held a hunger strike that lasted weeks, demanding improved conditions and an end to incarceration without formal charges or a trial, known as administrative detention. Fears of widespread unrest if a prisoner died were averted after the prisoners signed an agreement with the Israeli authorities.

But the latest hunger strikes have renewed those fears. Over the past few days, Palestinians have held rallies in support of the prisoners in several West Bank cities. On Tuesday, scores of protesters clashed with Israeli soldiers outside a military detention facility on the outskirts of Ramallah for the second time in a week. Some of the protesters had set out from outside the Ramallah office of the International Committee of the Red Cross.

Two of the hunger strikers, Mr. Issawi and Ayman Sharawna, were serving long terms in Israeli prisons before they were released early, in October 2011, as part of an exchange for a captive Israeli soldier, Gilad Shalit. They were rearrested last year after Israel said they had violated the terms of their early release.

Both had served several years of their original terms of about 30 years by the time they were released in the Shalit deal.

Israel has not given details of the alleged violations that led to their rearrest, but under a special military order, the two could be forced to serve the rest of their original sentences, amounting to 20 years or more for each of them. Several human rights lawyers said they were planning to file a petition in the Israeli Supreme Court on Wednesday against the military order, which allows for a special military committee to send released prisoners back to serve out their original terms based on secret evidence.

Saeb Erekat, a senior Palestinian official, said he had been appealing to the Israel authorities to help defuse the growing crisis.

“The situation on the ground now is really like a pressure cooker,” Mr. Erekat said in a telephone interview from Ramallah. “I urge Israel to release these people. The last thing we want is for things to get out of hand before President Obama visits.”

The two other hunger strikers, Tariq Qaadan and Jafar Ezzedine, are being held in administrative detention.

In addition, the Palestinian leadership is demanding the release of 123 Palestinian prisoners who have been held in Israeli jails since before the Oslo peace accord was signed in 1993.