By Philip Blenkinsop

Belgian-Brazilian brewer InBev filed a lawsuit late Thursday seeking to generate shareholder pressure for a takeover deal just before Anheuser dismissed its proposed $46.3 billion takeover bid as inadequate in a letter to InBev.

"We will carefully study the letter and will respond in due course," an InBev spokeswoman said.

The St Louis-based brewer's board unanimously rejected the Belgian company's $65 a share bid to create the world's largest brewer, saying the offer undervalued its assets and its growth plan, including a newly revamped cost-cutting program.

However, it also said it was open to considering any proposal offering full value to its shareholders.

InBev late on Thursday reiterated its preference for a friendly combination but filed a lawsuit to establish that shareholders could remove Anheuser's entire board of directors, in a possible prelude to a more acrimonious campaign.

InBev could not say when it expected the Delaware Chancery Court to rule, but believed it could come relatively soon. Anheuser is registered in the State of Delaware.

"It has a record of making decisions in a timely fashion," the InBev's spokeswoman said.

Analysts believe InBev, brewer of Stella Artois, Beck's and Brahma, will not give up its bid to add Budweiser and Michelob to its stable of global brands and say it can afford to pay more if required -- certainly $70 per share and possibly up to $75.

KBC Securities analyst Wim Hoste said InBev had two options: either to raise its offer towards $70 per share or go hostile at the existing $65, with a preference for the former.

"I can imagine they might try through informal contact to see if there is scope to talk about an offer. If not then they would take the hostile route," he said. "But the friendly approach is clearly better for public opinion and the workforce. The company is a U.S. icon."

Some U.S. lawmakers, including both senators from Missouri, have already expressed objections to the deal, arguing it could lead to U.S. job losses.

If the deal goes through it will be the third-largest foreign takeover of a U.S. company ever, as well as the largest takeover this year.

InBev has been keen to remind shareholders that its offer is 24 percent higher than the stock's closing price the day before reports that InBev was working on a bid surfaced and 35 percent above the average share price over the preceding month.

Anheuser's shareholder base has likely changed since InBev made its offer and is now populated with merger arbitrageurs who would be more receptive to InBev's advances.

InBev's shares were down 2.2 percent at 44.10 euros at 8:25 a.m. EDT in an overall weaker market. The DJ Stoxx European food and beverage index was 1.8 percent lower.

(Reporting by Philip Blenkinsop; Editing by David Jones)