WASHINGTON — With runaway health care costs reaching new heights, President-elect Bill Clinton's top advisers are telling him that managed competition, the centerpiece of his reform plan, will not slow national health spending appreciably for three to five years, sources said Wednesday.

As a result, Clinton's health care advisers are urging him to begin immediately the even more daunting task of creating a national board to impose limits on health care spending.

The apparent change of heart threatens to delay the unveiling of Clinton's health care reform package, which the President-elect had promised in the first 100 days of his Administration. Nevertheless, a top transition health care official insisted Wednesday that the incoming Administration still has December in mind as a target date for the signing of legislation to overhaul the nation's health care system.

Originally, Clinton had hoped first to implement the less controversial but still sweeping plan known as managed competition. Such a system relies on a mixture of government regulations and free market incentives to nudge employers and individuals into large purchasing networks. It then requires those networks to compete both on price and the quality of service they offer. The hope is the competition will result in lower prices while keeping quality high. Had that approach alone seemed likely to extend coverage to more people while still reining in the cost of health care--which reached $838.5 billion last year--Clinton might have been able to delay or avoid creating a national budget-setting board, sources said.

But with the transition team's projections of three to five years before costs can be stemmed under managed competition, there is little choice but to press on with the "budgeting mechanism," one top transition health care adviser said Wednesday.

Clinton talked throughout the campaign of creating a "health standards board" to establish annual health budgets and it is that notion which remains the single most controversial point in his health care reform agenda.

Most physicians and hospitals vigorously oppose such a board, fearing that regulation would lower their income. Analysts also fear that attempts to create such a board would generate so much resistance that all attempts at health care reform, including managed competition, would be derailed.