WHEN Congress returns from its summer recess next month, overhauling the nation's banking system will be a top item on the agenda.But a danger lurks that the urgency of the most agreed-upon aspect of the legislation - a replenishment of the nearly insolvent fund that insures commercial bank deposits - could derail plans for a broader reform of depression-era laws, say congressional and independent banking analysts. The question is how urgently the Bank Insurance Fund (BIF) needs to be replenished. The answer may come Tuesday, when the General Accounting Office and the Congressional Budget Office deliver prognoses on the funding level of the BIF. If the offices project the BIF will become insolvent by the end of September, Congress will have to act immediately to keep it funded - and may lose its momentum for more comprehensive reform. But if the two offices say the BIF will be out of money by the end of the year, that allows some breathing space to iron out more contentious issues in the reform, such as whether to allow commercial/industrial companies to buy banks and how far to allow banks into the securities business. In the event Congress needs to act quickly, the House Banking Committee has written a smaller, separate bill that deals chiefly with BIF refunding and reform of the deposit insurance system. The Senate Banking Committee has not prepared such a contingency plan; an aide to the committee insists the full Senate is capable of completing legislation for a comprehensive reform, including BIF refunding, by the end of September. The aide cites past years as a precedent, when efforts at banking reform have cleared the Senate only to run aground in the House, whose committee structure requires the proposed banking reforms to go through four committees. In congressional testimony July 31, Treasury Secretary Nicholas Brady warned against instituting reform bit by bit. "A thin, piecemeal approach is likely to push our most pressing problems into the future and could well defeat the very purpose of the legislation, which is to strengthen the banking and financial system and better serve consumers," he said. "Congress doesn't need more time to think about this," says Cynthia Glassman, director of research at the financial consulting firm Furash & Co. "They've had years of studies and hearings, and now it's time to act." Despite the hurdles ahead, the Bush administration and Congress's Democratic leaders say they are keen to finish banking reform this year. Over the 1980s, the nation's commercial banking system grew weak as other businesses got into lending and banks got caught up in risky ventures, such as junk bonds, overpriced real estate, and loans to third-world nations. Heightened consumer confidence in commercial banks would help the economy, and a strengthened banking system would make United States banks more co mpetitive globally. The House and Senate have already reached consensus on certain areas. Both agree that the Treasury can lend the BIF, which is run by the Federal Deposit Insurance Corporation (FDIC), $70 billion on a long-term basis, to be repaid by premiums from banks. Both would also strengthen regulation of banks in an effort to close those that are failing before they become insolvent. Large banks would be less likely to be deemed "too big to fail." Both houses would also allow banks to open branches nationwide, thou gh the Senate would allow individual states to vote against branching in their state. A key area of disagreement is over the proposal to allow commercial businesses to own banks, a cornerstone of the Bush administration's reform package. The House committee voted in favor, but the Senate committee voted against on the strength of vehement opposition to it by the committee's chairman, Sen. Donald Riegle (D) of Michigan. The House Energy and Commerce Committee, which is reviewing the legislation, has threatened to reverse the position on mixing commerce and banking. Proponents tout the idea as a way to inject voluntary capital into the banks, thus cutting back on the need for taxpayer money to bail out the industry. Banks would also potentially get new management used to working in a competitive environment. Opponents fear that allowing commercial businesses to own banks would make for too much concentration of money and power, which would be risky for the economy. Dr. Glassman calls such concerns "a kneejerk emotional response." She says: "The Germans and the Japanese allow businesses to own banks, and they have strong and healthy economies." But she believes the proposal will not pass in this country. Both houses' banking committees approved provisions permitting banks to use their capital to finance their affiliated securities operations, though the House bill provides for stricter "fire walls" between the banks and their securities affiliates.