UPDATE 2-Valeant boosts $53.8 bln Allergan bid as Ackman opts for stock

(Adds deal value, analysts' comments, closing share prices, background)

May 30 (Reuters) - Valeant Pharmaceuticals International Inc said on Friday it would boost its takeover bid for Botox-maker Allergan Inc for the second time this week, contingent on the two sides negotiating.

Laval, Quebec-based Valeant said it would pay $72 in cash - up from $58.30 on Wednesday - and 0.83 share of Valeant stock for each Allergan share. The revised, unsolicited offer was triggered by Pershing Square, the hedge fund controlled by Bill Ackman that is Allergan's biggest shareholder, agreeing to take only stock in Valeant for its Allergan shares.

The offer is worth $53.8 billion, up from Wednesday's $49.9 billion bid.

Allergan shares closed 5.7 percent higher at $167.46 while Valeant shares were 1.6 percent higher at C$142.43.

BMO analyst David Maris said the revised offer will fall short, adding it seemed "odd and erratic" that Valeant would raise the bid two days after its chief executive, Mike Pearson, promised not to negotiate against himself.

"Like with marriages in olden days, when a dowry rises rapidly and without reason, you should take a closer look at the bride," Maris said.

But analyst Ronny Gal of Bernstein Research said the offer increases pressure on Allergan to take action to raise the company's value and also to negotiate with Valeant.

"The offer now appears credible," he said. "We do not think this is a 'done deal' by a long shot, but obviously the likelihood of success is higher now."

Allergan was not immediately available for comment. It is best known for its lucrative Botox medicine, which is injected into muscles to smooth wrinkles.

Ackman said he called Pearson on Friday morning and offered to take stock for his Allergan shares if Pearson increased the cash offer to other shareholders.

"We believe that our gesture to the other Allergan owners makes an extraordinarily strong statement about our belief in the long-term value of this highly strategic business combination," Ackman said in a statement.

The deal value is based on Allergan's 303.5 million diluted shares outstanding as of March 31, 2014, and Ackman's holding of 28,878,638 shares.

The revised offer comes despite Pearson's earlier assertion that Allergan shareholders have told him they want more Valeant stock in the deal.

The company on Wednesday raised the cash component of its bid for Allergan, but the offer fell short of expectations and both stocks dropped.

Buying Allergan would push Valeant closer to its goal of becoming a top-five pharmaceutical company by market cap before the end of 2016, although Pearson also mused on Wednesday about potentially breaking up the company if that move produced more shareholder value.

Allergan has not yet responded to the earlier bid, other than to say it would consider it. The California-based company has criticized the sustainability of Valeant's rapid growth through acquisitions, which included contact lens maker Bausch + Lomb last year.

(Reporting by Rod Nickel in Winnipeg, Manitoba; Ransdell Pierson and Caroline Humer in New York; editing by Chris Reese, Marguerita Choy and Matthew Lewis)