Right- hander Aaron Cook, the veteran of the Rockies' homegrown rotation, has been offered a three- year contract extension in a move to try to keep the nucleus of the team together long term.

The Rockies already exercised their $4.5 million option on Cook for 2008. But he could be a free agent after the season, and the Rockies are hoping three years of additional security will entice him to make a commitment.

The Rockies are offering a $30 million guarantee with an option year, a source told the Rocky.

Cook has indicated a desire to remain with the Rockies, and while he would be giving up some money in exchange for the contract security, he also would be 32 when the extension expired and would have another opportunity to test free agency if he wanted.

A year ago, the Rockies signed Jeff Francis to a four-year, $13.25 million contract even though he was one year short of being arbitration eligible.

The Rockies also are expected to try to sign left fielder Matt Holliday to a multiyear deal. There have been indications a four-year proposal could be made worth up to $60 million.

Cook, a second-round draft choice in 1997, is second in seniority in the organization to first baseman Todd Helton.

Cook was the Opening Day pitcher in 2007 and went 8-7 with a 4.12 ERA in 25 starts, missing the final seven weeks of the regular season and the first two rounds of the playoffs with a strained left oblique muscle.