By Todd Wallack, Globe Staff

The offer from his credit card company last year was too good for Bob Leonard to refuse: checks he could use to borrow money at 3 percent interest and a promise the rate wouldn’t change “until the balance is paid off.’’

So for an upfront fee of 3 percent, the 47-year-old software executive used the checks to charge nearly $40,000 to his credit card for renovations to his home in Medford.

But then the card company, JPMorgan Chase & Co., hit him and more than 300,000 people who took the promotion with an additional $10 monthly service charge beginning in January. Chase also more than doubled the required minimum payment, from 2 percent of the monthly balance to 5 percent, increasing Leonard’s minimum to more than $1,500 per month, from about $600.

So Leonard drew down a home equity line of credit he had with his bank to reduce the amount he owed Chase.

“Apparently they don’t give a hoot about good will,’’ he said. “I’m done with Chase.’’

A Chase spokeswoman said the increase in minimum payments was necessary because some borrowers of the promotion were taking too long to pay off their loans. The company, said spokeswoman Gail Hurdis, is being a “responsible, careful lender.’’

Chase is but one of a number of major credit card companies that are jacking up interest rates and fees, or laying the groundwork to do so, before new federal legislation that cracks down on some of the practices goes into effect in February.

Bank of America, Chase, and Discover Card have switched many of their cards from fixed to variable interest rates that are tied to an underlying index. But since benchmark indexes are extremely low - the prime rate is near zero - analysts said credit card interest rates will almost certainly go up in the future.

Fees on foreign transactions have also increased. In May, Discover enacted a 2 percent foreign transaction fee. And some companies, including Bank of America, now levy a 3 percent transaction fee even if you buy an item online in US dollars, such as airline tickets, if the company happens to be based overseas.

Chase also recently raised the fee for balance transfers by 2 percentage points, to 5 percent of the amount moved. Others increased the rate by one percentage point.

Increases in credit card fees are not new. Credit card companies reaped $19 billion from late fees and other penalties on consumers last year, up 78 percent since 2003, according to R.K. Hammer, a financial consulting firm.

Credit card companies said they need to adjust costs because of economic circumstance and new regulations that will make it harder to modify rates in the future.

“The repricing enables us to preserve the safety and soundness of our business while continuing to lend,’’ Discover said in a statement.

Bank of America said its changes, including moving to a variable rate, are in response to the new federal law. “It will enable us to continue to extend credit to credit-worthy customers while remaining prudent in our lending practices,’’ said spokeswoman Betty Riess.

But the higher costs are hitting customers particularly hard now, with rising unemployment, wage reductions, and other cutbacks leaving some consumers struggling to pay bills. Moreover, some cardholders can no longer just jump to another card company, because lenders have tightened their standards and are refusing new customers or limiting their borrowing.

“A lot of people are trapped,’’ said Josh Frank, a senior researcher at the Center for Responsible Lending in Durham, N.C.

Frank and other watchdogs said credit card companies are trying to recoup losses. Credit card charge-offs - loans the banks do not expect to be repaid - rose to a record 10.76 percent in June in the United States and are expected to keep rising through mid-2010, according to a report that Moody’s Investors Service issued Wednesday American Express alone reported a $200 million loss at its US credit card unit last quarter.

“Their loss rates are going up and they are raising rates to compensate for the rising losses,’’ Frank said.

Moreover, the new federal legislation that Congress passed prevents companies from raising fixed rates on existing balances, unless a promotional rate ends or customers are late on their payments. New variable-rate cards will automatically adjust according to their benchmark.

“They’re trying to get their last licks in,’’ said Chi Chi Wu, a staff attorney with the National Consumer Law Center in Boston, which lobbied for the law.

Earlier this month, US Senator Chris Dodd, chairman of the Senate Banking Committee, asked federal regulators to make sure card companies comply with the new rules, including one that requires companies to reduce any rate increases imposed after Jan. 1, 2009, if they can no longer be justified. Dodd said he was particularly concerned that companies are raising rates now to skirt the new rules.

“I urge you to do everything in your power to protect cardholders from these abusive practices,’’ Dodd wrote.

Among card companies Chase has sparked many complaints with its “life of the balance’’ offer, according to Consumer Action, a San Francisco advocacy group that tracks credit card fees.

Many customers told the organization they feel Chase pulled a “bait and switch,’’ said spokesman Joseph Ridout. “People read the fine print, but Chase essentially erased all the fine print and changed the terms. It’s a brazen attempt to sidestep the reforms that are on the way.’’

Chase originally offered a low-interest rate for balance transfers and other amounts charged to its credit cards until the balance was paid off. Although customers were required to pay a transaction fee, they were promised they could retain the promotional rate - typically around 3 percent to 4 percent interest - so long as they paid off at least 2 percent of the balance each month.

But Chase then determined that some of the borrowers in the promotion took too long to repay, and increased the minimum payment amount, to 5 percent, and imposed the $10 monthly charge - although it was rescinded after Attorney General Andrew M. Cuomo of New York complained.

“Tens of millions of Chase customers have taken advantage of our promotional low-rate financing over the last five years,’’ and most have paid it back within two years, said Hurdis, the Chase spokeswoman. “However, there have been a small percentage of customers that have not made as much progress in paying down these loans. Our desire is to have these balances paid back in a reasonable period of time.’’

The new federal legislation will give state officials greater enforcement powers on credit card complaints. Massachusetts Attorney General Martha Coakley said she is ready to act.

“We’ve received complaints about credit card companies for a long time and our ability to respond has been limited,’’ Coakley said. Now, “if we believe there is a pattern [of problems], we will be more than prepared’’ to take action.