Be careful to protect retirement
Still, borrowers can get into trouble easily when using the lines of credit because college comes at a crucial time for most parents.

Ryan notes that people using them to pay for a child's education generally aren't too far from retiring. By putting more debt on their homes, they will reduce or eliminate its accumulated equity -- potentially wiping out a prime source of retirement income, since retirees tend to sell big properties to move into smaller, cheaper homes.

"It's a seemingly painless way to pay for college education, but I think the real problem won't become apparent until 10 or 20 years down the road when retirement is looming," says Ryan. "You're starting all over again with those mortgage payments, so you're right back to square one."

House may be at risk
While home equity loans often are a good last resort for parents who have been unable or unwilling to save, they subject homeowners to the whims of the housing market, the vagaries of interest rates and the volatility of their own personal finances -- needless risks for those with plenty of time to save.

Look at other sources
Planners also say families who qualify for government loans should take them rather than using home equity. "Your interest rate is clearly better than you'd get doing a home equity line," says Patti Houlihan, CFP, president and CEO of Houlihan Financial Resource Group in Reston, Va. The first payments also won't be due until six or nine months after the student finishes classes.

Parents in such a situation can choose from Perkins, Stafford and PLUS loans, each of which have different terms, conditions and borrowing limits. Perkins rates are generally the lowest at a fixed 5 percent, while the other two, which are tied to the movements of different Treasury bills, are currently a bit higher.

As a final caution, planners also suggest students contribute some of their own income from a job or other source to their education because it will give them a financial stake in the matter.