Most Americans believe gasoline prices will increase 21 percent this year and 63 percent say the price jumps so far have already caused them financial hardship, according to a Gallup poll conducted March 14-16. Forty-nine percent say prices will rise to the $3.76 to $4 per gallon range and 19 percent fear they will go over $4. the Lundberg Survey of 5,000 gasoline stations reported yesterday that prices rose nearly 7 cents over the past two weeks to reach an all-time inflation-adjusted high of $3.26 per gallon of self-serve regular.