The president says he's confident Britons, like Americans, "will not be intimidated by thugs and assassins."
His words of support for Londoners came after this month's second wave of attacks on the mass transit system.
The president said no one will "frighten us from our great love of freedom."
As for Mr. Bush's push to privatize Social Security, the president received a little help from his mother.
Former first lady Barbara Bush teamed up with her son the president on Friday in trying to drum up support among older Americans for his Social Security and Medicare plans.
He called his 80-year-old mother "my favorite senior citizen," and she tartly reminded him that at age 59 he was almost one himself with hair starting to turn white.
"You can see where I got my white hair from," the president retorted.
At a senior center, and then before an invitation-only audience at a downtown civic center, the mother and son team promoted Mr. Bush's embattled Social Security restructuring plan and the new Medicare prescription drug program that takes effect Jan. 1.
And like a vaudeville team, they kept stepping on each other's lines and zinging each other.
At the Wesley Woods senior center, both Bushes emphasized the importance of getting seniors to sign up for the new prescription drug plan, part of a Medicare restructuring enacted in December 2003.