Kerry will spend several hours in the western city of Jeddah consulting with the leadership of the oil-rich monarchy, which has been outspoken in its opposition to embattled Syrian President Bashar al Assad.
President Barack Obama is cautious about deeper US involvement in the increasingly sectarian conflict but has vowed to step up support for the rebels after concluding that Assad defied warnings and used chemical weapons.
US policymakers have privately voiced concern that Saudi Arabia and fellow monarchy Qatar could increasingly embrace guerrillas in strategically placed Syria if Western powers leave a vacuum.
Kerry told a conference of major powers in Qatar on Saturday that the United States and its partners were boosting military aid to Syria's mainstream rebels, although he has been reticent on the exact nature of the assistance.
In interviews ahead of his departure to Jeddah, Kerry declined to raise concerns about potential Saudi and Qatari support for hardliners but said it was critical to strengthen moderate rebels to prevent an Assad victory.
"If the United States does nothing, and the rest of the world does nothing, then Syria is going to wind up in an even worse condition than it is today," Kerry told CBS News from New Delhi.
A worse scenario in Syria could include "a total breakup, with radicals, extremists able to get a hold of chemical weapons and free to use it as a base to begin to conduct their operations again against the West and the United States," Kerry said.
Kerry has called for greater support to Syria's rebels by accusing Iran of "internationalisation" of the conflict through the growing role in the war of guerrillas from Hezbollah.
Kerry has insisted that the United States is not looking necessarily for a victory by the rebels but instead wants to step up pressure on Assad until he agrees to peace negotiations as set out by a conference in Geneva last year.
Russia, a supporter of the Assad family's four-decade rule in Syria, joined the United States in backing the Geneva plan.
While the United States has hailed the stance as cooperation by Russia, Kerry's trip comes amid a showdown as Washington demands Moscow turn over former US security contractor Edward Snowden who is wanted for exposing vast US surveillance operations.
Snowden fled Hong Kong to Russia in hopes of reaching a friendly Latin American nation but he then mysteriously disappeared.
Kerry will meet in Jeddah with Saudi Foreign Minister Prince Saud al Faisal as well as Prince Bandar bin Sultan, the kingdom's intelligence chief who was formerly ambassador to the United States.
Kerry will head later Tuesday to Kuwait, another US-allied monarchy, and then this week will go to Jordan in a new bid at making peace between Israel and the Palestinians.
He was returning to the region after three days in India, where he pledged to work toward stronger ties between the world's two largest democracies and promised to respect New Delhi's concerns over any US reconciliation with Afghanistan's Taliban.
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"US policymakers have privately voiced concern that Saudi Arabia and fellow monarchy Qatar could increasingly embrace guerrillas" Latest support for Taliban points in the same direction. All this wealth is going towards militant hardliners rather than supporting humanity. People from KSA and QATAR travel to west in need of good education, treatment or quality of life. They do not have the best University or Hospital in the World. They have the best guerrillas in the world. For Pakistan, Taliban will be lot more violent organization with current support. Stay tune for more turbulent years in the region. I predict that current monarch of KSA and Qatar will be the last monarch and Arab Spring is just around the corner. What goes around comes around.