Presidential contest between the advertising agencies takes shape.

On a political foray into Texas before Labor Day, Walter Mondale assured a sympathetic crowd that it wouldn't be the pollsters or advertisers who would decide the next president of the United States.

And in Little Rock, Ark., recently, Mr. Mondale declared: ''I don't want 1984 to be a contest between advertising agencies.''

That may be his desire, but pollsters and admakers for both parties are gearing up anyway. The presidential race looks as if it will be as much a contest between advertising agencies as between ideologies and politicians.

Between now and November, the two major parties may spend $500 million for everything from bumper stickers and buttons to commercials in prime time on national television, one industry source says. That is a boon to the advertising industry. The largest piece of the pie, about $250 million, will go to the broadcast media: the three major networks and independent TV and radio stations around the country.

In past years, critics have questioned the propriety of advertising that packages a candidate like a bar of soap. That is still a concern, but this year there's a different question making the rounds in ad circles.

Many are wondering if the Democrats' enthusiastic but untried advertising group headquartered in Washington will be any match for the highly polished ''Tuesday Team,'' the group of advertising professionals the Republicans assembled early this year in the heart of Manhattan's adland.

The Tuesday Team was put together expressly for the purpose of reelecting Ronald Reagan and George Bush. Under the leadership of its president, James D. Travis, who is on loan from Della Femina, Travisano & Partners, a major New York-based agency, the Tuesday Team is creating more than 75 television spots and hundreds of newspaper ads for the Republicans. The group is also responsible for selecting and buying tens of millions of dollars of television time.

The Tuesday Team is credited with creating the warm, emotional television commercials for the Reagan-Bush ticket which aired in May at a cost of $2 million. It also placed advertising spots featuring the President, which cost another $600,000 on television, around the time of the Democratic convention in San Francisco.

''We'll be covering the Republican convention in Dallas ... and looking for film footage we can use,'' Mr. Travis says. Most of the ads will focus directly on Mr. Reagan, he says, ''because the man conveys his convictions better than anyone else.''

There has been speculation that the Republicans might use video footage of Democrats squabbling in the primaries to make hard-hitting negative commercials.

''The Democrats trash each other,'' Travis says, ''but the President has a record of accomplishment.''

Meanwhile, the Democrats' advertising group, ''Consultants '84,'' has a more immediate concern than negative TV spots. It recently moved its headquarters from Austin, Texas, and is still organizing for the race ahead. Consultants '84 was started by Roy Spence, an executive from the Texas-based Gurasich, Spence, Darilek & McClure (GSD&M) agency.

Mr. Spence piloted Walter Mondale through his primary battles and is credited with the final cut of the film shown at the Democratic convention. Spence, who helped Mondale polish his acceptance speech, indicates that the Democrats' media efforts will be oriented toward the family, the impact of the deficit, education , budget cuts, and arms control.

''I think Geraldine Ferraro will play a prominent role. She adds a dimension to the campaign that opens up a whole new avenue of opportunity,'' Spence says. ''She symbolizes family, and we're going to be searching for topics like family that unite America in the truest sense.''

The big problem now for Consultants '84 is that it's still recruiting advertising professionals to put its $40 million to $50 million worth of TV messages across. But help is on the way. Last week it was announced that McCaffrey & McCall, a large New York agency, had been asked to work with Roy Spence and his group on a cooperative basis in media selection as well as creating TV spots for the Democrats.

Although many politicians decry the increasing reliance on expensive but cost-effective TV spots, few would dream of doing without it. In a recent survey of both Democratic and Republican politicians conducted by Vitt Media International, an advertising buying service, and St. John's University of New York, nearly two-thirds of those polled preferred TV for their campaign advertising.

Another result of this survey that surprised some advertising people was the growing popularity of direct mail. Nearly three-fourths (74 percent) of the politicians responding indicated they were using or planned to use it for soliciting contributions.

''Direct mail is coming on like gangbusters,'' says Hal Katz, Vitt's executive vice-president. ''It's fabulous. Politicians are using direct mail to raise the campaign funds they need to pay for the television they feel gets them elected.''