The White House will have 30 hours over two long days to present its defense of President Clinton. But the House Judiciary panel made clear yesterday it would not be deterred from starting a debate this week on whether the President should be impeached. The White House had asked for up to four days to make its case, but the House Judiciary Committee countered yesterday with an offer of two 15-hour days. If the full House votes to impeach the President, the Senate will hold a trial. A two-thirds vote would be needed to remove him from office.