For the second election in a row, Texas Democrats are placing a $1 million bet on Dan McClung, a seemingly unassuming consultant whose specialty is going head to head -- or computer to computer -- in a political battle for votes against the Republican Party.

The first gamble paid off in 1982 when McClung engineered a get-out-the-vote program that helped defeat incumbent Republican Gov. William Clements and brought in a slate of progressive Democrats to statewide offices.

Clements had a $7 million advantage over his Democratic challenger, Mark White, and what looked like a solid lead in the polls. But 800,000 more voters turned out in 1982 than in 1978, and White beat Clements by 231,575 votes.

This year McClung faces a much tougher test.

In polls, Walter F. Mondale is running as much as 30 points behind President Reagan in Texas and the Democratic Senate nominee, state Sen. Lloyd Doggett, trails the GOP candidate, Rep. Phil Gramm, by 10 to 15 points.

But in long-range terms, Texas is serving as a testing ground for Democrats to determine the effectiveness of a highly centralized, party-run program to register and turn out voters.

This party-led approach is standard operating procedure for the GOP at a national level and in many states, but it is the exception for the Democratic Party.

The Reagan-Bush '84 Committee has targeted Texas for voter registration and a get-out-the-vote program. The GOP has raised $2 million through a special Texas Victory '84 committee, considerably more than the Democrats' budget here.

Republicans are seeking to build strength in a generally affluent, white community, while the McClung-Democratic Party operation is trying to increase political participation in a much poorer, heavily black and Hispanic population.

To do this, both parties start with the same base, the computerized list of all registered voters. After that, the process grows complex.

Democrats are creating a menu of names by meshing the voter list with commercial lists of all persons with phone numbers, the state's file of everyone with a driver's license, a census list of all Hispanic surnames, ZIP code analysis based on partisan voting histories and the names of all voters who cast ballots in the 1982 and 1984 Democratic primaries.

In a state where, until recently, Democratic candidates dominated elections but the Democratic Party was just a paper organization, the acquisition of this key information has strengthened the party, significantly increasing the leverage of Bob Slagle, party chairman.

Detailed knowledge of the electorate is a powerful commodity in politics, and the state party now is receiving significant contributions from its own candidates -- $5,000 from each Democrat running for Congress, for example.

This partial revitalization of the Texas Democratic Party was started over three years ago by Sen. Lloyd Bentsen (D-Tex.). Faced with a 1982 reelection contest, Bentsen orchestrated the creation of a $1.2 million fund to finance a major get-out-the-vote program and hired McClung.

For this election, McClung and his consulting firm have been hired by the state Democratic Party.

McClung and Slagle lucked into two bonanzas. The first was a gift to the party of a piece of land worth at least $600,000 from James Moore, an Austin developer (in Texas, there are no limits on the amount an individual can give to a state party), and the second was a list of all persons who received unemployment benefits over the past 18 months.

The state party has taken out a mortgage on the land to pay for about half the total cost of the voter registration and get-out-the-vote drive. The Democratic Victory Fund, a branch of the Democratic National Committee, has kicked in $300,000 so far, and officials here are hoping to persuade the committee to come up with at least another $300,000.

Officials of the Mondale-Ferraro campaign had appeared ready to drop support of the Texas drive when polls showed that Mondale was running far behind Reagan and that Hispanic support for Mondale was relatively weak -- only six of every 10.

More recently, however, Texas officials regained promises of cash support from the Victory Fund based on polls showing Mondale gains among Anglos after the Oct. 7 debate and on data showing that in 1982 Hispanics were leaning Democratic by only a 67-to-33 ratio in polls but on Election Day 86 percent voted Democratic.

The unemployment list provided a key target group for voter registration efforts. A registration form was mailed to everyone on the list, and many were called through a network of 15 Democratic phone banks operated by workers paid $3.50 to $4 an hour.

"There are 330 phones. We call from 5 p.m. to 9 p.m. Monday through Thursday, 9 a.m. to 5 p.m. on Saturday and noon to 8 p.m. on Sundays," Slagle said. "Friday is the night a lot of people go to high school football games here."

In addition to the people collecting unemployment benefits, McClung used combinations of names and voting histories to produce a list of unregistered persons living in "high profile" Democratic ZIP codes where past Democratic margins exceeded 65 percent. Most of these areas are black or Hispanic.

An attempt was made to call everyone -- 500,000 households -- on this second list. For those interested in registering, the Democratic workers would fill out a registration form for them, except for the signature, during the phone call. The form was then sent to the prospective voter, who only had to sign it and put it, post-paid and addressed, into a mailbox.

With the registration period over, the state party is in the midst of the second stage: the persuasion of marginal voters. This involves a very complex maneuver designed to identify swing voters -- those who split their tickets between candidates of both parties in the past -- who are "persuadable," not locked into voting Republican this year.

McClung took every precinct that cast 50 percent or more of its votes for Clements, the GOP candidate for governor in 1982, and at minimum 50 percent of its vote for a Democratic candidate in any other contest. The result was a list of 500,000 households.

The ZIP codes for all these voters, almost all of whom are white, were then shipped off to Claritas, a Washington firm, where they were broken down into 10 demographic "clusters" according to income, age, number of school-age children, blue or white collar employment, value of home, owners and renters, and so forth.

William R. Hamilton and Staff Inc., a Bethesda polling firm, then surveyed samples of 75 in each of the clusters to find what McClung called "any angle we might get them to move our way." The issues range from state spending on education to the deficit and Equal Rights Amendment.

From this, the Democrats will produce about six different letters designed to appeal to each group. Each group then will receive three different mailings, McClung said.

Before the "persuasion" phase is completed, the party will begin the final get-out-the-vote (GOTV) process, a system designed to identify clearly Democratic voters and make sure they get to the polls.

Automatically qualifying for the "GOTV file" are residents of precincts with 65 percent or better Democratic voting histories. The tougher problem is locating Democratic voters in precincts with lower Democratic margins. To do this, the list of all voters in precincts casting 55 to 65 percent of their votes for White in 1982 is first combed through for Hispanic names, which, on the assumption that they will cast strong majorities for Democrats, automatically go into the GOTV file.

Blacks automatically go into the GOTV file, and blacks and Hispanics are asked by phone if they are willing to volunteer to call 15 others on Election Day.

With whites, many of whom are expected to vote Republican, the operators of the phone bank will ask a "test question" likely to be: "Can we tell Lloyd Doggett he can count on your support?" McClung said. "I think using Mondale would cost us too much" unless Mondale makes signficant headway in the polls, he added.

"Then there will be a mailing of about 1.3 million to everybody we've been able to identify by race or by them telling us on the phone that they are with us. We are not trying to persuade this crowd. We're just trying to get them to vote."

In a separate move, the Democratic Party will send absentee ballots to every black and Hispanic over 65, plus selected Anglo voters.

As Election Day approaches, the phone banks are to move into high gear calling voters in solidly Democratic precincts and those who said by phone they will vote Democratic. In addition, the party has budgeted about $80,000 for paid workers to spend 20,000 hours knocking on doors.

On Nov. 6, the army of door knockers and phone bank operators gets shifted throughout the day to precincts across the state where turnout is lower than expected.

Slagle contends that this kind of intensive drive can make a 5 to 10 percentage-point difference in a race, a shift that, given current poll findings in Texas in the presidential race, would not be adequate for Mondale to win the 29 electoral votes here. But the strength of the Democratic and Republican registration and GOTV drives may well determine the outcome of the Senate race.