The Senate has displayed a general deference toward the Obama administration’s foreign policy in the past four years, but it could become a far more raucous and combative place if Foreign Relations Chairman John Kerry is tapped to join the Cabinet.

The Massachusetts Democrat is on President Barack Obama’s short list for secretary of State or Defense, and Kerry would almost certainly breeze through confirmation (unlike another possible nominee for State, U.N. Ambassador Susan E. Rice).

But the White House may start to have second thoughts about nominating Kerry as it envisions a chamber that could be more willing to challenge Obama on a range of issues, from Iran to Cuba.

If Kerry leaves, the chairmanship of Foreign Relations would probably fall to Sen. Robert Menendez, the combative New Jersey Democrat. Although California Democrat Barbara Boxer stands next in line after Kerry in seniority, she is unlikely to give up her position as chairwoman of the Environment and Public Works Committee.

“If the chair opens up, it will go to Menendez, no question,” said a Democratic member of the committee, who spoke on condition of anonymity to discuss internal committee dynamics.

The difference in style between Kerry and Menendez couldn’t be greater. The patrician Kerry is known for his diplomatic skills, his long, detailed speeches, and his loyalty to Obama on foreign policy issues. Menendez, the only Hispanic Democrat in the Senate, is blunt and an aggressive interrogator during hearings. He also doesn’t mind going against the administration, as he has done over the past year in pushing — and winning — ever tougher sanctions against Iran.

“He’s a bull in a china shop, a street fighter,” said a senior aide for the Senate Banking Committee, on which Menendez also serves.

The focus of the Foreign Relations committee likely would shift significantly under a Menendez chairmanship, panel aides say. Menendez, together with Illinois Republican Mark S. Kirk, is expected to continue his efforts to sanction Iran as punishment for continuing its nuclear enrichment program. Menendez led the charge over the past two years to cripple Iran’s economy — moves he says strengthen the administration’s hand in any negotiations with Iran but which some critics say only convince Tehran’s leaders that the real aim of the sanctions is to bring down the regime.

Since last December, the Senate overwhelmingly passed three rounds of Iran sanctions over the objections of the White House, which has sought to preserve its dominance over foreign policy.

Menendez, whose parents moved from Cuba to New York in 1953, also is expected to raise the profile of human rights abuses by the Castro regime in Cuba. Representing a major Cuban-American community in New Jersey, he has been an outspoken opponent of any moves to ease relations with Havana — something that could complicate any efforts by the Obama administration to reach out to Cuba in its second term.

The committee’s dynamics are going to change whether or not Kerry leaves. It’s losing ranking Republican Richard G. Lugar of Indiana, the Senate’s elder statesman in diplomatic and national security issues, who lost his primary this year and is leaving at the end of the 112th Congress. Bob Corker, a Tennessee Republican who has been more skeptical of key administration policies on Libya and Syria, for example, is expected to take his spot.

Another major change to the committee could come if Republican John McCain of Arizona joins its ranks. An outspoken voice who has pushed for more active intervention in Libya and Syria, as well for more muscular action to rein in Iran’s nuclear enrichment program, McCain has said he would like to join the panel. He will step down next year as ranking member of the Senate Armed Services Committee because of GOP term limits.

For the past two decades, the Foreign Relations panel has been known for an unusual degree of bipartisan cooperation, and Kerry has followed that model. During his tenure as chairman, Kerry joined forces with Lugar to concentrate on non-proliferation issues. Together they shepherded the New Strategic Arms Reduction Treaty through the Senate in 2010, further limiting U.S. and Russian nuclear warheads. The two also pushed through a multi-billion-dollar economic aid package to Pakistan.

Kerry also decided to wait until after the elections to hold any open hearings on the security mishaps surrounding the September attack on the U.S. mission in Benghazi, Libya, where U.S. ambassador J. Christopher Stevens and three other Americans were killed. He said he wanted to allow the State Department to conclude an independent review, which is due this month.

The Obama administration could well decide it cannot afford to lose Kerry’s calming presence and foreign policy expertise in the Senate. Kerry has been a member of the panel since 1985. Since taking over the chairmanship in 2009, he has also served as an unofficial troubleshooter for Obama, who has sent him to resolve thorny diplomatic issues in a number of hot spots.

For example, he was sent to Afghanistan in October 2009 to advance presidential elections after opponents of President Hamid Karzai attributed his victory to voter fraud. After spending hours talking with Karzai, Kerry finally convinced him to hold a runoff election. At the time, Karl Eikenberry, the U.S. ambassador to Afghanistan, said Kerry’s diplomatic skills, knowledge of the region and determination were “decisive.”

At Obama’s request, Kerry went to Pakistan to secure the release in early 2011 of CIA contractor Ray Davis, who was jailed after shooting several Pakistanis who reportedly tried to rob him. He also helped broker a peace agreement between Sudan and newly independent South Sudan.

Perhaps, Senate aides say, the strongest argument against a Kerry nomination is the possible loss of his Senate seat to Republican Scott P. Brown, who was defeated in November by Democrat Elizabeth Warren. Though a Brown victory is not certain in the special election that would follow any move by Kerry to the administration, the aides note Brown remains popular in the state and has a well-oiled campaign machine. A Brown victory would reduce the Democratic caucus majority in the Senate, which includes two independents, to 54 seats.

“Why take a chance?” one aide asked.

Emily Cadei contributed to this report.