Updated from 2:56 p.m. EDT

Billionaire financier Carl Icahn plans to buy at least $15 million of

General Motors

(GM) - Get Report

stock, the automaker announced Friday, less than a month after he announced a similar deal to acquire shares of a laser eye surgery company.

Shares of GM promptly rose 3, or 4.6%, to close at 68 7/16 Friday, as the company repeated its belief that its stock is undervalued. The company, with a stock market value of about $37 billion, has watched its shares fall well off their 52-week high of 94 5/8.

Icahn, a New York City native known for acquiring big stakes of companies and then demanding changes aimed at stimulating managers and stock prices alike, told GM that he sought to acquire up to 15% of the company's outstanding shares. Based on Friday's closing share price, a stake of that size would cost about $5.5 billion.

Detroit-based GM, confronted with Icahn's advances, said it remains dedicated to maximizing value for shareholders.

GM noted that it is continuing with its $1.4 billion stock repurchase program, and it highlighted a gradual effort to trim its stake in

Hughes Electronics

(GMH)

. GM earlier this year allowed its shareholders to exchange its shares for stakes of Hughes tracking stock. GM has reduced its interest in Hughes from 60% to 30%, according to the company.

Hoping to unlock the potential of Hughes, investors have urged the company to sell or spin off the division, which includes the satellite television business

DirecTV

. But GM has said in the past that it does not intend to separate the unit.

Wheel and Deal

In late July, Icahn made a similar move, announcing his intention to acquire $15 million, but less than 15%, of stock in

Visx

(VISX)

, the laser vision correction technology firm. Icahn did not return telephone calls to his New York City office.

Shares of Santa Clara, Calif.-based Visx surged 15% in the first day of trading after the announcement, but have since fallen a bit, closing Thursday at 24 9/16. On Friday, Visx stock, which has plummeted from a 52-week high of 100 1/4, declined 1/8, or .5%, to 24 7/16.

It's widely acknowledged that Icahn has a keen eye for a bargain, but one analyst, Mark C. Johnson of

A.G. Edwards& Sons

, questioned whether GM is as undervalued as some Wall Street observers -- and maybe Icahn -- believe. Consider other companies in the automotive realm, like

Ford Motor

(F) - Get Report

and auto parts firms

Dana

(DCN)

and

Johnson Controls

(JCI) - Get Report

, all of which have watched their share prices slump in recent months, he said.

Grappling with uncertainty over interest rates and future auto sales, many companies in the automotive sector are trading at much lower prices. Auto sales are peaking, Johnson explained, and sagging stock prices simply reflect investors' concerns about slower growth in upcoming quarters.

"General Motors is not unique," Johnson said. "If GM was down 40%, and other stocks were up 10%, then yeah, I'd jump on the undervalued bandwagon, too." Johnson rates GM a "maintain," and his firm has not done any underwriting for the company.

It's unlikely Icahn is thinking about

price/earnings ratios. "He's probably thinking about something else," said Jonathan Lawrence, an analyst at

Dain Rauscher Wessels

. Maybe Icahn is positioning himself for a potentially lucrative spin off of the Hughes division -- or perhaps he wants to make a bid to take over the unit himself, Lawrence said. His firm has not done any underwriting for GM.

Icahn, who has a nearly 10% stake in

Nabisco Group Holdings

(NGH)

, made a bid last month for the company, which holds almost 81% of snack-food maker

Nabisco Holdings

(NA)

.

He later made a profit of roughly $600 million when

Philip Morris

(MO) - Get Report

, owner of

Kraft Foods

, agreed to buy Nabisco Holdings for

$14.9 billion. In addition, Nabisco Group Holdings agreed to be sold to

R.J. Reynolds Tobacco

(RJR)

for $9.8 billion.

Icahn, who also said recently he wanted to make a big investment in retailer

J.C. Penney

(JCP) - Get Report

, gained a great deal of attention during the 1980s as a corporate raider who made huge profits from investments in companies like

Texaco

(TX) - Get Report

and

Phillips Petroleum

(P)

. He also bought

Trans World Airlines

(TWA)

, which was later sold.

GM received a letter from Icahn on Wednesday, and afterward a senior executive with the company met with the financier to discuss his intentions to acquire the shares, said Toni Simonetti, a spokeswoman for GM.

Visx adopted a shareholders rights plan, a defensive maneuver otherwise known as a "poison pill," in response to Ichan's move, but GM does not have such a plan at this point, Simonetti said.

John F. Smith Jr., GM's chairman, said in a statement the company had returned more than $34 billion to its shareholders in the last three years. That figure includes $9 billion in stock repurchases and $9 billion from a spinoff of its

Delphi

automotive business, Simonetti said.