With Congress taking its first stab in five years at rewriting the drug approval process, the Senate began considering a bill that could become a magnet for all sorts of prescription drug proposals.

The measure (S 1082) taken up by the Senate Monday is considered must-pass legislation by the drug industry, which says it is necessary to keep the flow of new drugs entering the market.

But it’s also a high priority for Democrats in Congress, who have seen other parts of their health care agenda stall.

The bipartisan measure is sponsored by Massachusetts Democrat Edward M. Kennedy, chairman of the Health, Education, Labor and Pensions Committee, and is backed by the panel’s top Republican, Michael B. Enzi of Wyoming.

But bill supporters will have to fend off attacks from multiple flanks. Enzi acknowledged Monday that the language Kennedy presented as a manager’s amendment won’t be the final product.

“This is a work in progress,” he said on on the floor. “We’re not there yet. We’re close.”

Critics of the bill’s drug safety provisions, led by Charles E. Grassley, R-Iowa, want to create an independent office of drug safety within the Food and Drug Administration (FDA). Grassley has written a bill (S 468) with Christopher J. Dodd, D-Conn., that would do just that.

Grassley has argued extensively that the bill’s drug safety monitoring provisions do not go far enough. A spokesman for Grassley said staff were working on addressing a number of his concerns and he would likely offer a floor amendment on drug safety.

Other amendments could come from supporters of a prescription drug importation bill (S 242) introduced in January by Byron L. Dorgan, D-N.D., that has 31 cosponsors, including Kennedy and Grassley. A spokesman for Dorgan said Monday that negotiations were continuing on whether he would offer the importation bill as an amendment.

Other lawmakers have discussed adding language that would legalize generic biological products, also known as “biosimilar” drugs and follow-on biologics. Unlike many drugs, biologics are complex biological molecules difficult to replicate and do not currently have generic alternatives. A generics provision would treat them more like other drugs, in that once their patents expire, generics makers could move in with copies.

The bill’s provisions to tighten FDA control over direct-to-consumer advertisements for drugs could also be a target for amendment. Opponents of the ads claim they artificially drive up demand for drugs and interfere with the doctor-patient relationship.

Foes of giving the FDA extended authority call it a First Amendment issue.

Pat Roberts, R-Kan., has promised to fight the bill’s advertising restrictions, which would give the FDA stricter power to review and approve ads. In an April 18 markup, he offered an amendment to trim the FDA’s authority under the bill. It was rejected.

“I’m not going to go down without a fight when this bill hits the floor,” Roberts told Kennedy during the markup. “I do not think it’s constitutional.”

Roberts likely will have an ally in Tom Coburn, R-Okla., the Senate’s only practicing medical doctor. “I don’t like it as a physician,” Coburn said of the advertising. “But you’re going to have a hard time passing a First Amendment test saying a drug company can’t advertise its drugs on television.”

Democrats have promoted a broad range of health care proposals since taking the reins of Congress in January but so far have had little success in enacting their agenda.

Among the items:

• Language allowing the importation of drugs from several countries faces a veto if passed as stand-alone legislation and is in search of a must-pass bill to carry it into law.

• Embryonic stem cell research legislation (S 5, HR 3) has passed both chambers but faces a presidential veto. Supporters don’t have enough votes in either chamber to override the veto.

• A bill (S 3) allowing the government to negotiate prescription drug prices fell short of the 60 votes necessary to cut off debate in the Senate.

• Health information technology legislation has not yet been marked up, after being passed in both chambers last year but never making it to conference.

The FDA program that Kennedy’s bill would reauthorize reviews and monitors the development of new pharmaceutical products and monitors the safety of the drugs once they are in use.

Industry fees paid to the FDA as part of the program guarantee expedited review times to get drugs to market faster.

Critics of the bill argue that the industry fees have become such a critical part of funding as to leave the FDA beholden to the industry. Kennedy has said he would like to give the program more direct government funding but that the fees are a fact of life for now.

His legislation includes language that would reauthorize a similar program for the approval of medical devices, which also collects user fees from device makers to expedite the approval process.