RIVERSIDE, Calif.  The Jordanian business partner of a prominent Florida businessman, who has raised more than $500,000 for Senator John McCain, appears to be at the center of a cluster of questionable donations to his presidential campaign.

Campaign finance records show Mr. McCain collected a little more than $50,000 in March from members of a single extended family, the Abdullahs, in California and several of their friends.

Amid a sea of contributions to the McCain campaign, the Abdullahs stand out. The checks come not from the usual exclusive coastal addresses, but from relatively hardscrabble inland towns like Downey and Colton. The donations are also startling because of their size: several donors initially wrote checks of $9,200, exceeding the $2,300 limit for an individual gift.

Making matters murkier, some couples in the family who contributed more than $9,000 to Mr. McCain also gave the maximum in December to either Senator Hillary Rodham Clinton or Rudolph W. Giuliani, or both, totaling in the case of at least one family more than $18,000.