Rules that President Bush proposed yesterday to make it easier for Americans to buy generic drugs were swiftly challenged by key lawmakers and consumer representatives, who contended that the plan would not adequately rein in the pharmaceutical industry, was politically timed and might not go into effect for years -- if at all.

Critics on and off Capitol Hill also accused the White House of stealth and said that administration officials had concealed their intentions, even at a House hearing on the generic drug issue this month, until the first business day after Congress left Washington.

Others contended that the White House's approach, which relies on a change to Food and Drug Administration regulations, would allow a Republican administration, which has opposed stronger legislation pending in Congress, to command attention and credit on a popular issue two weeks before the midterm elections.

"Frankly, the proposal . . . is an insult to American consumers," said Rep. Sherrod Brown (Ohio), the lead Democratic sponsor of generic drug legislation that passed the Senate July 31 but has not been brought to a vote by the House's GOP leadership. The bill overlaps the administration's plan in certain respects but contains several features Bush does not support that would make it more difficult for brand-name drug companies to keep generics out of the market -- and more powerful enforcement methods if companies flout the rules.

"Three weeks before the election, the administration suddenly has a change of heart and issues a proposed regulation," Brown said. "As opposed to new laws, which the White House could have proposed but did not, new regulations typically take at least two years to implement."

The intense reaction came as Bush announced the proposal, previewed by administration officials the night before, to restrict the ability of companies that make brand-name drugs to stave off competition from companies that produce lower-price generic equivalents.

The president and his aides portrayed the administration's approach as a strategy that balances the need for affordable medicine with a desire to preserve economic incentives for brand-name drug makers to invest in new therapies. "Unfortunately, the careful balance of the law is being undermined" by loopholes used by brand-name companies under the current system, Bush said during a morning Rose Garden ceremony.

"Our message to brand-name manufacturers is clear," he said. "You deserve the fair rewards of your research and development; you do not have the right to keep generic drugs off the market for frivolous reasons."

Bush called the proposal "another important advance in the cause of bringing affordable prescription drugs to our seniors," a constituency of prime importance in the elections that will determine which political party controls Congress. He said the changes would have the same effect for Americans of all ages.

Specifically, the proposal would make it more difficult for companies that make brand-name drugs to get repeated delays -- or "stays" -- when manufacturers of generic drugs challenge their patents in order to get onto the market. Lately, that practice has blocked for years generic equivalents of several of the nation's best-selling drugs, according to a study issued last summer by the Federal Trade Commission.

In addition, the proposal would forbid brand-name companies from getting new patents for three kinds of reasons, including redesigned pill packages, that the FTC concluded were frivolous and used mainly to forestall competition.

The White House's announcement was praised by several parts of the health insurance industry, the AARP, some congressional Republicans and -- to some degree -- by the generic drug manufacturers. Even critics said that Bush had drawn useful attention to the problem.

Some lawmakers questioned whether the FDA had the legal ability to make these changes through a regulation. Sen. Orrin G. Hatch (R-Utah), an author of the 1984 law covering drug patents, praised the administration's ideas as "carefully crafted." But, he said, "it may be preferable for Congress to enact legislation in this area," noting that courts have found in several recent cases that the FDA has overstepped its legal bounds.

Critics noted that, while Bush said his plan put the FTC recommendations into effect, that agency actually had suggested that Congress make changes to patent law, rather than the FDA change its regulations.

Several congressional aides were more pointed, speculating that the White House, reluctant to antagonize the pharmaceutical industry, which has been a leading donor for GOP candidates, had chosen a route that was legally questionable, so that the industry could sue -- and thus prevent the changes from taking effect.

Marc J. Scheineson, an FDA official a decade ago who now is a Washington attorney specializing in food and drug law, said that he believed the administration probably was on solid legal ground, but that legal challenges delaying the rules nevertheless were likely. "The incentive for industry to litigate is enormous," he said.

The main trade group that represents brand-name drug companies, which has vigorously resisted other attempts to foster competition from generics, was one of few organizations that withheld comment. Jeff Trewitt, a spokesman for the Pharmaceutical Research and Manufacturers of America, said merely that the proposal was "complex" and was being reviewed. He said the group had never considered whether the FDA had the power to make such changes -- or whether the organization would challenge the proposal.

An administration official said that the White House had consulted heavily with FDA attorneys before concluding that the agency has the necessary authority -- and predicted that the rules could be in place relatively early next year. Even if the rules prompted a lawsuit, the official said, "Congress can always revisit this next year."

President Bush announces generic drug plan with Health and Human Services head Tommy G. Thompson.