The Democratic congressmen, Brian Baird of Washington and Keith Ellison of Minnesota, were in Gaza early Thursday, the U.S. consulate said.
Consulate spokeswoman Micaela Schweitzer-Bluhm said the lawmakers would meet with U.N. officials. There were no plans to meet with Hamas, which the U.S. shuns as a terrorist group.
Visits by U.S. officials to Gaza have been rare since Palestinian militants blew up an American diplomatic convoy in October 2003, killing three people, and no American representatives have gone since Hamas won Palestinian elections in 2006. The group violently seized control of Gaza the following year.
Since taking office last month, President Obama has repeatedly said he hopes to improve U.S. relations with the Muslim world. As the first Muslim member of Congress, Ellison could play a key role in that mission. He could not immediately be reached for comment.
The visit comes in the wake of a fierce Israeli military offensive last month. The three-week operation, launched to end years of Palestinian rocket attacks, killed some 1,300 Palestinians, caused widespread destruction and left thousands of people homeless.
Several U.N. facilities, including a large warehouse at the organization's Gaza headquarters, were heavily damaged. The U.N. has been trying to raise emergency funds to meet what it says are dire humanitarian needs in Gaza following the offensive.
i government spokesman Mark Regev said he had no knowledge of the lawmakers' Gaza visit.
Meanwhile, Israeli politics dealt what could be a severe blow to the Obama administration's renewed effort to negotiate a Mideast peace deal.
Far-right Israeli politician Avigdor Lieberman endorsed Benjamin Netanyahu for prime minister on Thursday, all but guaranteeing that Netanyahu, a vocal critic of talks with the Palestinians, will be the country's next leader.
The divisive Lieberman has emerged as the kingmaker of Israeli politics after the Feb. 10 election produced a deadlock between its two largest parties, and his backing of Netanyahu could be basis for a hardline government.
Lieberman's Yisrael Beitenu Party finished third, essentially allowing him to determine whether Netanyahu or his chief rival, Foreign Minister Tzipi Livni, would be able to form a parliamentary majority.
Lieberman has raised eyebrows around the world with his calls to make Israel's Arab minority swear loyalty to the state or lose their citizenship.
Lieberman announced his decision in a meeting with President Shimon Peres, who is holding consultations with political parties this week before choosing a candidate to form a government.
He told Peres that Netanyahu's Likud Party should head the new government, but that he supports a broad coalition that includes Livni's centrist Kadima Party as well.
"We need a wide government with the three big parties, Likud, Kadima and Yisrael Beiteinu," he said. "Netanyahu will lead the government but it will be a government of Netanyahu and Livni together."
Kadima edged out Likud in the election, capturing 28 seats compared to 27 for Likud. But in the 120-seat parliament, Likud is in a better position to put together a coalition because of gains by Lieberman and other hard-line parties. It could be several weeks before a coalition is finally formed.
Netanyahu has said he would turn to his "natural" allies among the religious and nationalist parties in parliament. But he has said he also hopes to bring in more centrist parties to create a wide coalition with broad national consensus.
After Lieberman's announcement, Kadima officials said they were likely headed toward the opposition. Kadima leads the lame-duck government, and Livni had campaigned on pledges to continue peace efforts with the Palestinians.
"If Kadima will join a government like this, based on these guidelines, Kadima will be wiped off the political map," Kadima Cabinet Minister Meir Sheetrit told Israel Radio. "Kadima can be the only alternative to the Likud reign in the future."
Another Kadima Cabinet Minister Zeev Boim, said Kadima would not serve as a "fig leaf" for a hardline government.
A narrow hardline government led by Netanyahu could hurt Israel's standing in the world and place it on a possible collision course with President Obama, who has said Mideast peacemaking will be a top priority of his administration.
The government would likely freeze peace talks with the Palestinians, draw international pressure and face dissatisfaction from large parts of the Israeli public. It will also give smaller partners veto power over major decisions because they would be able to topple the government at will, indicating the government will be short-lived.
Peres began his political consultations with Likud and Kadima representatives on Wednesday. He was meeting representatives of the 10 other elected parties on Thursday to hear their choice for prime minister.
If neither Netanyahu nor Livni were to garner the support of a majority, Peres was expected to encourage the two to share the premiership.
However, after Lieberman's endorsement of Netanyahu, a "rotation" at prime minister appears unlikely, and Netanyahu is poised to return to Israel's top post a decade after he was ousted from it.
Once named by Peres, Netanyahu will have six weeks to build a coalition government.