Billionaire investor Carl Icahn wants Navistar International Corp (NAV.N) to consider merging with rival Oshkosh Corp (OSK.N), though he has not yet made a formal proposal to either company, several people familiar with the situation said.

Icahn, who has amassed 10 percent stakes in each of the companies, is currently in discussions with Navistar about getting one or more seats on the board of the U.S. truck and engine maker, these people said.

Icahn reported his stake in Navistar last week and said at the time he has held talks with management to discuss its business strategies and will seek additional conversations. [ID:nN1E79C21X]

A deal, however, is far from certain. It's not clear whether either of the companies would be open to the idea and it remains to be seen how effective Icahn would be in getting what he wants at these companies.

Shares of Oshkosh, which have nearly halved this year as the company struggles with a declining defense business and an expensive 2006 acquisition of JLG Industries, jumped 6.6 percent to $19.61 on the New York Stock Exchange on Friday, valuing the firm at nearly $1.8 billion.

Navistar shares rose 3.6 percent to $41.53 in early trading, valuing the company at about $3 billion. The stock has fallen some 30 percent this year.

A Navistar-Oshkosh combination has long been talked about as a possibility in the industry as the two companies can wring out costs and excess capacity. There are also some complementary units such as Navistar's finance and engine making businesses that could benefit from a merger.

Oshkosh investors have been concerned about the company's exposure to defense contracts due to government-spending cutbacks and increased competition, including the threat posed by Navistar's own plan to grow in the sector.

Tying up with another player in the heavy-vehicle industry could protect Oshkosh from a secular downturn in the defense sector that many analysts are predicting.

Icahn did not return a request for comment. Oshkosh declined to comment on relationships with Icahn and other shareholders.

A Navistar spokesperson referred to remarks its chief executive Dan Ustian made in an interview with Fox Business on Tuesday. In that interview, Ustian said Icahn is into (Navistar) to make some money... We have to deliver to him and all our other investors.

Icahn purchased his Oshkosh stake in June, when shares in the Wisconsin company were trading considerably higher.

Shares in mid-June, prior to Icahn's disclosure, were trading near $25 a share. By the time he started snapping up Navistar, Oshkosh shares were trading in the mid teens.

The corporate raider-turned-activist has had some high-profile disappointments this year in fights at Lions Gate Entertainment Corp (LGF.N), Clorox Co (CLX.N) and Forest Labs (FRX.N).

But Icahn was also the biggest individual holder of El Paso (EP.N), which agreed to be bought by Kinder Morgan (KMI.N) earlier this week.

He also saw his years-long investment in Motorola turn around earlier this year when Google Inc (GOOG.O) agreed to buy Motorola Mobility Holdings Inc (MMI.N) for $12.5 billion.

(Reporting by Soyoung Kim, John D. Stoll and Paritosh Bansal, editing by Dave Zimmerman)