The board of directors at BEA Systems told activist shareholder Carl Icahn in a letter Monday that they would sign off "immediately" on a takeover offer from Oracle that values the company at $21 per share.

The board, however, maintained its position that Oracle's previous $17-per-share offer -- which expired Sunday -- "significantly undervalues" the business software maker.

"We will continue to vigorously oppose a sale to Oracle or anyone else at that price," the board said in the letter, a copy of which was posted on BEA's Web site.

Icahn, a billionaire who owns more than 13% of BEA, has been pressuring the company's board to put Oracle's offer to a shareholder vote. To date, the board has resisted.

In its Monday letter to Icahn, BEA's board -- which includes company founder and CEO Alfred Chuang and Google CFO George Reyes -- said it's prepared "to sign immediately" a merger agreement that values the company at $21 per share, or $8.3 billion in total.

"It's important that there be no misunderstanding of the board's position. We are opposed to selling the company at $17.00 per share. We are not opposed to selling the company," said the board members said in the letter.

BEA's board may be hoping that a larger player -- say, IBM or Hewlett-Packard -- will step in to outbid Oracle.

Oracle has said it wants to acquire BEA in order to integrate the company's middleware technology into its own products. Specifically, Oracle said it wants to get its hands on BEA products that help businesses build service-oriented architectures.

Increasingly popular in corporate data centers, a SOA is a highly efficient software infrastructure in which computer code can be reused and redeployed as needed, saving on development costs.

Oracle announced its intention to buy BEA for a total of $6.7 billion on Oct. 12. At the time, president Charles Phillips said Oracle would continue to support BEA's existing products if a deal was consummated.

Editor's note: This story was updated at 11:35 a.m. to correct the title of Charles Phillips.