Updated

President Bush announced new rules Monday aimed at keeping drug makers from extending their patents on drugs, a strategy that prevents generics from reaching the market sooner and keeps prescription drug costs inflated.

"This is another important advancement in the cause of bringing more affordable prescription medicines to our seniors," Bush said in a morning appearance in the White House Rose Garden.

The new rule, similar to legislation that passed overwhelmingly in the Senate, will limit drug makers to a single 30-month extension of their patents -- provided under the 1984 Hatch-Waxman Act -- rather than allowing drug companies to reapply for copyright status based on minor alterations such as the drug's appearance.

"When a drug patent is about to expire, one method some companies use is to file a brand new patent, based on a minor feature such as the color of the pill bottle of a specific combination of ingredients unrelated to the drug's effectiveness. In this way, the brand name company buys time through repeated delays," Bush said.

The president rejected the generic drugs bill that had passed the Senate with more than three-quarters' support from the body, saying that it created unacceptable liability provisions.

Patents on several top brand-name drugs, including Zocor, Paxil, Flonase and Cipro, are set to expire in the coming months.

Administration officials said the Federal Trade Commission found eight cases over the past 10 years in which drug companies were believed to have made frivolous claims to block generic drug competition.

That's a small fraction of the market, officials admit, but they say the practice has been on the rise, and they feared that with the many high-profile patents set to expire, a large number of legal challenges to generics would occur.

Prescription drugs are a perennial election issue and Democrats who learned of the proposal said it was a means for the president to claim some headlines without doing anything to get generic drugs on the shelves faster.

"This sounds like an Election Day conversion," said Sen. Charles Schumer, D-N.Y, sponsor of a Senate bill to limit lawsuits aimed at thwarting generic competition. "The devil will be in the details.

"This could be a very good proposal, but given the White House's track record on this issue, it could be just another loophole to let the name-brand drug companies delay the implementation of generic drugs," Schumer said.

"This is a small down payment, but no substitute for the more comprehensive generic drug legislation that died in the Republican-controlled House after it passed the Senate," said Sen. Ted Kennedy, D-Mass., who chairs the committee that deals with health issues.

The president's focus on a domestic political issue with two weeks left to the midterm election was not the plan, aides say, adding that Bush acted only now after Congress demonstrated that it wasn't going to get to this issue right away.

Americans spent $154 billion on prescription drugs last year. The average brand name drug costs $72 per prescription, more than four times as much as the average generic drug. About half of all prescription drugs are filled with generics, the White House said.

Bush said opening up the drug market will enable inventors to show off their successes by moving on to the next medical innovation.

The White House also was moving to tighten requirements and increase disclosure rules for drug patent listings. The administration is publishing its rule in the Federal Register, where the public can comment on the rule for 60 days before it becomes final.

It has the support of the Generic Pharmaceutical Association, which supports moves to reduce the delay in delivering affordable pharmaceuticals to consumers, said Kathleen D. Jaeger, the association's president.

Jackie Cottrell, a spokeswoman for the Pharmaceutical Research and Manufacturers of America, said the brand-name trade group would defer comment until after the official announcement.

Fox News' Wendell Goler and the Associated Press contributed to this report.