"We make sure there are assurances in place, in general, sufficient to satisfy us that the deal is appropriate from a national security standpoint," Chertoff said on ABC's "This Week."
London-based Peninsular and Oriental Steam Navigation Co., was bought last week by Dubai Ports World, a state-owned business from the United Arab Emirates. Peninsular and Oriental runs major commercial operations in New York, New Jersey, Baltimore, New Orleans, Miami and Philadelphia.
U.S. lawmakers from both parties are questioning the sale, approved by the Bush administration, as a possible risk to national security.
"It's unbelievably tone deaf politically at this point in our history," Sen. Lindsay Graham, R-S.C. said on "Fox News Sunday."
"Most Americans are scratching their heads, wondering why this company from this region now," Graham said.
Added Sen. Evan Bayh, D-Ind.: "I think we've got to look into this company. We've got to ensure the American people that their national security interests are going to be protected."
At least one Senate oversight hearing is planned for later this month.
"Congress is welcome to look at this and can get classified briefings," Chertoff told CNN's "Late Edition."
"We have to balance the paramount urgency of security against the fact that we still want to have a robust global trading system," he added.
Sen. Robert Menendez, who is working on legislation to prohibit companies owned or controlled by foreign governments from running port operation in the U.S., said Chertoff's comments showed him that the administration "just does not get it."
In a statement, the New Jersey Democrat said, "No matter what steps the administration claims it has secretly taken, it is an unacceptable risk to turn control of our ports over to a foreign government, particularly one with a troubling history. We cannot depend on promises a foreign government has given the administration in secret to secure our ports."
Chertoff said Dubai Ports World should not be excluded automatically from such a deal because it is based in the UAE.
Critics have cited the UAE's history as an operational and financial base for the hijackers who carried out the attacks of Sept. 11, 2001.
In addition, they contend the UAE was an important transfer point for shipments of smuggled nuclear components sent to Iran, North Korea and Libya by a Pakistani scientist.
DP World has said it intends to "maintain and, where appropriate, enhance current security arrangements." The UAE's foreign minister has described his country as an important U.S. ally in fighting terrorism.
Meanwhile, a company at the Port of Miami has sued to block the takeover of shipping operations there by Dubai Ports World.
The Miami company, a subsidiary of Eller & Company Inc., presently is a business partner with London-based Peninsular and Oriental Steam Navigation Co. In a lawsuit in Florida circuit court, the Miami subsidiary said that under the sale it will become an "involuntary partner" with Dubai's government and it may seek more than $10 million in damages.
The Miami subsidiary, Continental Stevedoring & Terminals Inc., said the sale to Dubai was prohibited under its partnership agreement with the British firm and "may endanger the national security of the United States." It asked a judge to block the takeover and said it does not believe the company, Florida or the U.S. government can ensure Dubai Ports World's compliance with American security rules.
CBS News reports that Baltimore Mayor O'Malley, who co-chairs the U.S. Conference of Mayors' Task Force on Homeland Security, is calling on President Bush to reverse the decision.
O'Malley harshly criticized the president's approval of the ports deal as an "outrageous, reckless and irresponsible decision" and urged the White House to reconsider the sale. Baltimore is one of the affected ports. O'Malley also is running for the Democratic gubernatorial nomination in Maryland.
In New York, families of some victims from the September 2001 terror attacks were critical of the deal. New York Senator Charles Schumer said he is dubious any assurances can justify involvement by the United Arab Emirates in American ports.
Schumer and other critics have cited the UAE's history as an operational and financial base for the hijackers who carried out the attacks against New York and Washington.
"A lot of families are incensed by this, because you're talking about the safety of the country," said William Doyle, whose son Joseph died at the World Trade Center. "We have a problem already in our ports because all of our containers aren't checked, but now they want to add this unknown? It's not right."