CAIRO, Egypt — Palestinian Arabs swelled across the Egyptian border for a second day yesterday as diplomats sought to avert a political and humanitarian crisis. President Mubarak of Egypt asked his government to send food and supplies to stores and aid organizations in towns along the Gaza Strip border.

The Egyptian state-owned satellite channel Nile News quoted anonymous security sources as saying that as many as 500,000 Palestinian Arabs, one-third of Gaza’s population, had crossed into Egypt since the border wall was breached Wednesday. Much to the dismay of Israeli and American officials, Egypt has made no effort to reseal the border.

Exact figures on the number of Palestinian Arabs crossing the border was impossible to ascertain as Egypt and Hamas, the radical Islamist group that controls Gaza, and other Middle East capitals have vested interests in inflating figures to pressure Israel, which cut fuel supplies to the coastal strip in reaction to continued attacks. But there was a sense of urgency in America to end the miles-long processions of trucks, taxis, and donkey carts streaming across the Rafah border.

Undersecretary of State Nicholas Burns of America told reporters that officials were in contact with Egypt and were prepared to assist it in bringing stability to the Sinai.

“Our view is that order should be restored to the border,” Mr. Burns told reporters in Jerusalem, adding that services should quickly be re-established to Gaza’s 1.5 million residents.

Egyptians are historically sympathetic to Palestinian Arabs, “so the crisis boosts Mubarak’s image, but on the other hand problems can arise,” a political analyst with the Al Ahram Center for Political and Strategic Studies in Cairo, Gamal Abdel Gawad, said. “There is no security at the border, and all kinds of people are flowing freely.”