There is a new aggressiveness about GTE Corp. that has charmed Wall Street, made an impact in Washington, and raised the possibility that the conglomerate with $21 billion in assets is on the verge of waking from decades of dozing.

As part of the maneuvering, this summer the corporation's name was changed from staid-sounding General Telephone & Electronic Corp. to GTE Cort. In part, the name change was designed to keep pace with the slick image of the company portrayed by the "Gee! No, GTE!" national advertising campaign.

But the changes are more than cosmetic. When the dominant American Telephone & Telegraph Co. splits apart in 1984, GTE, its second-ranked competitor in the telecommunications business, will become half the size of AT&T, rather than one-tenth as large as the Bell System as it is today. At that point, GTE is considered the likeliest competitive beneficiary of the Bell System's divestiture.

Launching its own satellite system, stepping up its telephone switching equipment sales domestically and abroad, upgrading historically poor relationships with residential customers, particularly in Southern California, moving its Vienna, Va., data communications subsidiary, Telenet, into profitability, and making a major push in cellular systems, the hot new mobile telephone technology, are just pieces of the GTE story.

"I think we're in an ideal posture," said Theodore Brophy, GTE's chairman and chief executive officer, during a recent interview at corporate headquarters here. "We have the freedom to participate in any of the businesses that either the Bell operating companies or AT&T can compete in. At the same time we're not faced with going through the traumatic reorganization that AT&T has to go through."

To add to its list of communications products and services, knowledgeable industry sources say GTE is also looking to purchase or invest in Southern Pacific Communications Corp., the microwave communications company that is a subsidiary of the troubled, cash-poor railroad. While spokesman for the two companies will not comment on the matter, other sources say the transaction, reportedly dubbed project "Featherbed" and GTE, would essentially complete what industry analysts say is a nearly full set of components of a total telecommunications package.

"GTE doesn't have all the pieces together yet," said John Chapman, a telecommunications analyst and vice president of The Gartner Group Inc., when asked about the possible deal. "They need SP if they are going to be a major player in voice traffic. They are going to need a long-haul microwave network."

Ironically, the possible bid for SP, which markets its long-distance service as Sprint, comes as the Southern Pacific unit is turning its first significant quarterly profits. Chapman estimated the service earned $18 million and $19 million for the first two quarters of 1982.

Though much has been made of GTE divestitures, particularly its 1980 jettisoning of Sylvania's television manufacturing operations, GTE seems poised today for major acquisitions. "You shouldn't be surrised if we make a major one" said GTE President and chief operating officer Thomas V. Vanderslice.

It was the arrival of Vanderslice in 1979 from an executive vice president's post at General Electric that really began to focus attention on GTE. He shook up management, and 55 percent of the top 107 managers at GTE are in new jobs since Jan. 1, 1981. "I think it is clear, without being unkind, that the company had outgrown some of its management," Vanderslice said. "GTE is a company that needs change, that's getting change and is getting it on a planned basis."

It is the nurturing of existing talent and the addition of new managers to GTE's ranks that has taken much of Vanderslice's energies. Today, Vanderslice and Brophy are convinced that the talent is in place to bring together GTE's disparate pieces, technologies as diverse as communications, plastics, and lighting products. If GTE was considered an industrial firm, rather than a utility, its assets would rank it would rank it as the nation's 10th-largest corporation.

Assuming the team is in place, then, it is the potential integration of flowering telecommunications technologies into a systems package that is GTE's current management challenge. Those prospects, Telenet's steady sales growth, and the coming on line of the company's first major digital telecommunications products have pushed Wall Street solidly into GTE's corner. Many analysts and rsearch firms are aggressively recommending GTE, predicting "explosive growth in non-telephone business," as Butcher & Singer Inc, did recently in putting GTE atop a list of "five stocks to buy now."

"We think the telephone industry in general has some problems ahead of it in its transition to a competitive state, but in the industry, GTE is well positioned," said Edward M. Greenberg, a telephone analyst with Sanford C. Bernstein & Co.

Greenberg, in what is a consensus Wall Street view, said that the Vanderslice management, improving profitability in the GTE Commuications Products Group, and a hoped-for recovery in the housing industry, which would boost GTE's sagging lighting business, all bode well for GTE's stock. He predicts the company's profits will rise from about $4.45 a share this year to about $5.25 a share in 1983.

But the political challenge for GTE is to do all that, raise its marketplace visibility, and at the same time avoid running afoul of antitrust enforcers and regulators who will be watching to see that GTE's complete integration does not pose the same kinds of economic threat that led to the move to break up AT&T.

In fact, GTE, in a fierce lobbying campaign directed at Federal Communications Commission members two years ago, who able to have overturned an FCC staff recommendation that would have forced GTE to split off its competitive, computer-like operations into a separate subsidiary. That lobbying skill has carried over to Capitol Hill, where Brophy and Rep. Timothy Wirth (D-Colo.) were close allies in the recent unsuccessful fight to pass legislation putting further restrictions on AT&T activities.

There are serious GTE watchers who will say that the philosophical view held by Justice department antitrust chief William Baxter, which suggested that AT&T's monopoly and competitive enterprises did not belong under the same unbrella, ultimately might be made to apply to GTE, too.

"They seem to have gotten off with rather little attention from regulators or anyone else because they never rose to the surface," said Walter Hinchman, a Reston, Va., consultant who is a former head of the FCC's Common Carrier Bureau.

"But in terms of size and integration they pose the same kinds of concerns. Maybe the divestitute of Bell will cause GTE to come to the surface. Most of the other companies in the industry are not major factors, but GTE is in manufacturing and in service and has the same potential problems that existed with Bell."

Chapman, a former Justice Department attorney, has a similar view of the AT&T-GTE comparison. "Whether you call GTE dominant or not, they have an effective monopoly in their territories and it would seem that Baxter would look at GTE and where he sees a bottleneck, that issue could be lurking in the wings," Chapman said. "The same issues are relevant to GTE".

On top of that, GTE's reputation in the communications marketplace is that of a rough, tough fighter. "They think that in a fundamental way they don't have much to fear," said a well-known communications GTE operations. "An awful lot of businessmen are abusive when you ask them about GTE. They carry a lot of baggage with them."

For example, GTE field representatives reportedly have stunned independent telephone and switchboard manfacturers by telling them GTE, a major market in the telecommunications industry, would no longer need their products, said this source. "The point is that at a critical juncture when they've won the right to compete without a separate subssidiary, they've become hard people to do business with," he said.

But the AT&T-GTE parallels do not strike Brophy as major issues. Each of the seven regional operating companies AT&T plans to spin off under the consent agreement with the Justice Department is larger "than the totality of GTE's telephone operations and we certainly don't have their power in interexchange [long distance]," Brophy pointed out. "We really don't have AT&T's market power."