Pharmaceutical giant Amgen is laying off about 450 of its Rhode Island employees, setting back efforts by state leaders to use the company as the foundation of a biotechnology industry in Rhode Island.

The layoffs, announced late yesterday, deprive the state of high-wage jobs at a time of sluggish employment growth and stagnant wages.

“This is the last thing we need,” Leonard Lardaro, an economist at the University of Rhode Island, said yesterday. “This was an area that we finally targeted as a niche, and it’s starting to falter.”

The staff at Amgen’s West Greenwich plant was notified yesterday that 1,500 employees nationwide would be laid off by early November, Amgen spokesman Larry Bernard said.

Those layoffs come less than a month after Amgen, based in Thousand Oaks, Calif., introduced a voluntary buyout package to cull its staff nationwide and in Rhode Island. The number of employees here peaked at 1,700.

The company has not disclosed how many Rhode Island staff members were among the 700 employees nationwide who opted for the buyout earlier this month. Those employees will leave Amgen by Nov. 16.

Overall, Amgen’s Rhode Island staff could be reduced by nearly one-third by next year.

The layoffs, planned for early November, were not unexpected.

After years of swiftly growing revenues and profits, the world’s largest biopharmaceutical company has seen sales of its two leading drugs, the anemia medications Aranesp and Epogen, plummet.

In March, the FDA issued a warning related to the drugs, citing studies that reported that patients taking them in higher-than-recommended dosages had an elevated risk of “life-threatening side effects and/or death.” The two drugs generated nearly half of Amgen’s sales of $14.3 billion last year.

Shareholders have punished Amgen stock. The share price has dropped nearly 40 percent from its two-year high of $84.42 in November 2005. The stock closed yesterday at $55.29, down 13 cents.

Sales of Enbrel, the drug Amgen produces in Rhode Island, have continued to grow during this period, reaching $2.9 billion last year. Enbrel is used for treating rheumatoid arthritis.

But as part of a company-wide effort to cut capital expenses by $1.9 billion — in part by eliminating as many as 2,600 positions — Chief Executive Officer Kevin Sharer decided to close one of Amgen’s two manufacturing plants in Rhode Island.

That decision means Rhode Island is bearing a disproportionate burden in the cost-cutting. Though Amgen’s 1,600 employees in Rhode Island make up 8 percent of its global workforce of more than 20,000, the state is accounting for 30 percent of all layoffs announced yesterday.

Bernard, Amgen’s spokesman, said the company has been satisfied with its operations in Rhode Island, where it has invested more than $1.5 billion since 2002. As recently as last spring Amgen was still growing here, adding more than 400 jobs.

In May, Amgen held its first annual shareholders’ meeting in Rhode Island, and Sharer praised the West Greenwich complex as “the best factory in the Amgen system.” Only days before, Amgen’s head of operations, Dennis Fenton, had predicted that the Rhode Island plants would outlast Enbrel production, citing plans to retrofit them for another drug if Enbrel sales drop after it loses patent protection.

Yesterday, the state’s top economic development official, Saul Kaplan, said Amgen’s struggles do not signal broader problems in the state’s economy.

“It is not a commentary on Rhode Island’s business climate,” Kaplan said. “We will weather this.”

Melissa L. Withers, a spokeswoman for the state Economic Development Corporation, said the state would help displaced workers find new jobs. “These are workers with important skills that we’re confident will find other opportunities in our economy,” she said.

That may prove challenging. Despite efforts by Governor Carcieri to challenge the dominance of Massachusetts in the biotechnology sector, Rhode Island’s biotechnology companies are largely small start-ups. The positions available tend to focus on research, not manufacturing, and often require a doctorate.

Alexion Pharmaceuticals, based in Cheshire, Conn., recently spent $47 million transforming the former Dow Chemical facility in Smithfield into a biomanufacturing plant for the drug Soliris. But it had filled its 100 openings before Amgen announced the buyouts and layoffs, and the company is not expected to grow significantly unless it develops a second drug.

The arrival of Amgen had been held out as proof that the state could compete for biotechnology firms, building on its manufacturing tradition to outmaneuver states competing with generous tax breaks and land grants. (In Rhode Island, Amgen was given a $9.3-million rebate on the sales taxes it paid for construction materials.)

But in June 2006, the state failed to persuade Bristol-Myers Squibb to build a $660-million drug manufacturing plant in the Quonset Business Park. After naming Rhode Island as a finalist, the company chose Devens, Mass., last summer.

A spokesman for Carcieri, Jeff Neal, was not available for comment late yesterday.

Rhode Island cannot afford to lose the jobs. With the national economy slowing, pulled down by a housing slump and tightening credit, Rhode Island saw its unemployment rate grow last month to 5.1 percent, with 28,800 people out of work. Job growth has been .75 percent this year; it usually averages about 1 percent on an annual basis. The state’s median income of about $37,000, meanwhile, trails the national average of about $40,500 making the Amgen cuts particularly sting. Amgen’s average wage in Rhode Island is about $55,000, and a handful of posts pay at least $80,000.

For now, both of Amgen’s Rhode Island plants are operating 24 hours a day to meet demand for Enbrel.

But Bernard said the original plant, known as BioNow, could be mothballed by the end of the year, permitting a range of staff reductions that were announced yesterday. “It’s not limited to manufacturing,” Bernard said yesterday. “All of the quality manufacturing scientific jobs, all of the trade jobs, all of the support and administrative functions are all impacted. There isn’t a single department where this is concentrated. It’s spread out across the site.”

bgedan@projo.com