CAMBRIDGE,Biogen, which has a major production facility in Research Triangle Park, and IDEC pharmaceuticals disclosed plants to merge the companies Monday morning before the stock markets opened.

The deal is worth some $6.8 billion.

Under the agreement, Biogen (Nasdaq: BGEN) shareholders will receive 1.150 shares of IDEC stock. IDEC shareholders will end up owning 50.5 percent of the merged company.

The new company will be called Biogen IDEC Inc.

Shares in Biogen were up 1.6 percent, to $44.50, in early hours traiding. IDEC traded up 31 cents to $39.28.

IDEC (Nasdaq: IDPH) is based in San Diego.

James Mullen, chairman and chief executive officer of Biogen, will be chief executive officer of the merged company. William Rastetter, head of IDEC, will be executive chairman.

The companies produced $1.5 billion in revenues in 2002 and have $1.55 billion in cash.

“Biogen and IDEC are two remarkably complementary companies in virtually every sense — therapeutic focus, R&D capabilities, manufacturing infrastructure and financial position,” Rastetter said in a statement.

The deal produces a company with more than $550 million in annual research and development funding as well as 1,000 employees focused on R&D. The companies said the merger would help them not only diverside product portfolios but also accelerate development of 10 new products.

The deal also should produce 15 percent annual revenue growth through 2007, according to the companies.