CHICAGO (AP) _ Bank One's new chief executive said Wednesday he's not inclined to sell the company's First USA credit-card unit or the banking company itself, despite problems that have sullied the bank's reputation.

``I came here only to build a great financial services company, not to sell it,'' Jamie Dimon said in an investor conference call.

He did not preclude a transaction later on, however.

In remarks that should hearten customers, he also declared that customer service must be improved in all of Bank One's businesses.

Dimon, named CEO and chairman of the nation's fifth largest bank holding company on March 27, has his hands full after taking a year off since departing his job as president of Citigroup Inc.

Chicago-based Bank One has endured rocky times since the disclosure last August that soaring growth in First USA, the country's No. 2 credit-card issuer, had slowed due to a series of flawed marketing strategies that drove existing customers off. The mistakes carved deeply into Bank One earnings and caused its stock to lose half its value.

But Bank One shares have been rallying since Dimon's hire, rising 25 percent in eight days and closing at $35.18 3/4 Wednesday on the New York Stock Exchange, a 56 1/4-cent gain.

That's an encouraging sign for Bank One, whose executives have insisted for months that its operations are healthy outside the well-publicized First USA troubles and that a turnaround should be completed by year's end.

It's also a whopping paper profit of $14 million for Dimon, who bought 2 million shares of Bank One stock on March 27 at $28.37 1/2 a share.

While avoiding specific details of his Bank One plans in what he called an introductory call, Dimon quickly dampened speculation that he might want to shed First USA as a quick fix for the company's woes.

``The fun for me is to make this a great American financial institution, and it certainly is a great platform to do that, in spite of some of the problems and stubbed toes and broken legs we may have had lately,'' he said.

``My quick read is this company's not ready to do deals right now,'' Dimon said.

Regarding First USA, he said ``I know what you know. I think clearly it is a serious thing, but I also look at the credit-card business as fundamentally a good business. I don't see any reason why we can't stabilize ours.

``Hopefully we'll be able to fix it.''

Dimon also said Wingspan, Bank One's Internet bank unit, ``did a lot of things right'' but spent too much money on bad advertising.

Addressing a topic that has hurt Bank One's image, he said ``We've got to do a better job in customer service. It's just so important to the current health of the franchise.''

As to his own decision to come back to a traditional banking operation rather than pursue offers to delve into an Internet business: ``I liked what I did, I like complexity, I like problems. Maybe I'm a masochist. ... I love the financial services business.''