James Dimon's second visit to Capitol Hill in a week to discuss multibillion-dollar trading losses quickly morphed into a discussion of swearing in, gambling and making millions on Wall Street.

Before the House Financial Services Committee could even get under way with its interrogation of Mr. Dimon, lawmakers quibbled about whether the chief executive of J.P. Morgan Chase & Co., the biggest U.S. bank, should take an oath and later about whether his testimony should be believed without a swearing-in. Mr. Dimon wasn't sworn in.

Overall, Mr. Dimon received far rougher treatment at the hands of the members of the House than he did a week ago in the Senate. Several accused Mr. Dimon of being more focused on trading activities tantamount to gambling than on lending to consumers.

Rep. Barney Frank (D., Mass.) declared himself 'disappointed' in Mr. Dimon not once but twice, then asked him if his compensation could be cut for not spotting the problems earlier.

Rep. Sean Duffy (R., Wis.) pushed Mr. Dimon on whether J.P. Morgan is 'too big to manage, too big to regulate, too big to control,' which Mr. Dimon denied. Mr. Duffy hit he bank for using excess deposits to make complex trades in London rather than 'investing those dollars here with American businesses.'

The lectures appeared to rankle Mr. Dimon. Certain questions received sharp, defiant retorts. 'We lost $2 billion to Chrysler. I assume you'd want us to continue to lend to Chrysler,' Mr. Dimon shot back when Rep. Gary Ackerman (D., N.Y.) suggested the bank's hedging amounted to gambling.

'We don't gamble,' Mr. Dimon said curtly. 'We do make mistakes.'

Most Republicans on the panel had more criticism for the panel of five regulators who testified earlier in the day for failing to catch wind of J.P. Morgan's disastrous losses earlier.

Under questioning by Rep. Randy Neugebauer (R., Texas), Comptroller of the Currency Thomas Curry acknowledged that his agency wasn't aware of 'the potential significance of the situation' until April 9, days before news reports about the 'London whale' -- the J.P. Morgan trader known for his outsize positions -- surfaced. Mr. Curry hadn't given such an exact answer before.

Mr. Dimon told the committee someone on his team briefed regulators 'right prior to April 13.' Monday, April 9, was a holiday in London, and markets didn't reopen until April 10. 'That day it lost $300 million was the first trading day after the article,' Mr. Dimon said. Asked to comment on the size of the loss, Mr. Dimon replied, 'I would considered that to be a small thing for J.P. Morgan.'

At the end of the hearing, a woman named Adriana Velasquez appeared and demanded to know why the bank doesn't pay its cleaning staff better. Surrounded by a throng of reporters, Mr. Dimon told her he would meet with her if she called his office. Ms. Velasquez said after the hearing that she was a janitor in a J.P. Morgan building in Houston, and that her union paid to fly her to Washington.

Alan Zibel / Victoria McGrane