CHICAGO (Reuters) - Industrial conglomerate Danaher Corp (NYSE:DHR - News) said on Monday it had agreed to buy electronic testing company Tektronix Inc (NYSE:TEK - News) for $2.8 billion to expand its product line.

Danaher, which also raised its third-quarter profit forecast, said it will pay $38 a share for Tektronix, a premium of 34 percent to Friday's closing price of $28.34 on the New York Stock Exchange.

Washington-based Danaher, whose portfolio also includes tools, dental equipment and product-identification technology, makes instruments for industrial, medical and other applications. Beaverton, Oregon-based Tektronix focuses on measuring and monitoring equipment for such industries as communications, computer, consumer electronics and education.

"Tektronix provides an excellent complement to our existing electronic test business," Danaher Chief Executive Lawrence Culp said in a statement.

"We believe we can continue to deliver strong results in our established businesses and look at attractive adjacent markets for future growth opportunities," he added.

Danaher said it expects third-quarter earnings before one-time items to be at or slightly above the high end of its previous forecast of 92 cents to 97 cents a share.

Analysts were expecting 97 cents a share, according to Reuters Estimates.

Danaher's forecast excludes about 4 cents a share from certain favorable tax items and an expected lower tax rate.

Tektronix, with annual revenue of $1.1 billion, would become part of Danaher's Electronic Test platform, joining Danaher's Fluke and Fluke Networks businesses, and nearly doubling the platform's revenues.

The deal, approved by Tektronix's board, is expected to close in the current quarter.

The deal will be a "fundamental change" under the terms of certain Tektronix notes, allowing noteholders to convert their notes into cash, the companies said.

(Reporting by Ben Klayman; additional reporting by Dane Hamilton in New York)