[SDL] Scrolling background

[Jan Kratochvil]

Hi,
 i tried to make scrolling background using SDL and i have to make some
terible mistake because it is teribly slow.
I am using resolution 800x600 (32b colors).
is there any better(faster) solution than using

SDL_BlitSurface(image, &src, screen, &dest);
SDL_UpdateRect(screen,0,0,0,0);

where src y coordinate is incrementing. If i call this two functions in
for cycle i get speed from 6 up to 10 frames per second.
Please help.
Thanx Jan Kratochvil