A bitter divide over the Middle East could threaten Democratic Party unity as representatives of Senator Bernie Sanders of Vermont vowed to upend what they see as the party’s lopsided support of Israel.

Two of the senator’s appointees to the party’s platform drafting committee, Cornel West and James Zogby, on Wednesday denounced Israel’s occupation of the West Bank and said they believed that rank-and-file Democrats no longer hewed to the party’s staunch support of the Israeli government. They said they would try to get their views incorporated into the platform, the party’s statement of core beliefs, at the Democratic National Convention in Philadelphia in July.

“Justice for Palestinians cannot be attained without the lifting of the occupation,” Dr. West, one of Mr. Sanders’s five representatives on the platform committee, said in an interview. Dr. West said that while he recognized the necessity to provide for the security of Jews, who for thousands of years have been a “hated people,” he thought that the platform needed to bring more balance to “the plight of an occupied people.”

The presence of Dr. Zogby and Dr. West on the 15-member panel, which also has six appointees of Hillary Clinton and four from the party chairwoman, does not guarantee their views will prevail. But it raises the prospect that one of the party’s most sensitive issues will be open to public debate while Mrs. Clinton is in a fight to unify her party and appeal to voters turned off by Donald J. Trump.