Two GOP presidential candidates, Sen. Robert J. Dole and former secretary of state Alexander M. Haig Jr., are having some bad moments after reports last Friday that a number of forged signatures on their candidate petitions in Texas might keep them off the primary election ballot and deprive them of any share of the state's rich bounty of 111 delegates to the Republican National Convention.

While Texas GOP officials said that as of now all six Republican candidates will be on the ballot pending validation of their qualifying petitions, the episode is the tip of a political iceberg that gets little public attention: the behind-the-scenes organizational nightmare of qualifying for ballot access and a full delegate slate in a number of crucial, big, early deadline campaign states such as Texas, Illinois and Pennsylvania.

Today is the deadline for qualifying delegates in Illinois, considered the toughest of all. All the presidential candidates of both parties who are determined to have full delegate slates in every state -- except Gary Hart -- have been working since last fall to put together slates in each of the state's congressional districts and get the requisite number of petition signatures to qualify them for the primary election ballot.

Because of previous mishaps, the candidates this year know the peril of not getting down to the nitty-gritty of this house-to-house political warfare. The bottom line in primary battles is not who wins the most popular votes; it is who wins the most convention delegates. In some key states, a candidate can win the popular votes and lose all or most of the delegates because he has failed to get onto the ballot slates of delegates pledged to him.

In 1980, for example, George Bush won the popular vote in the Pennsylvania presidential primary, but Ronald Reagan won the GOP delegates because of Bush's slating problems.

In his run for the 1984 Democratic presidential nomination, Hart neglected to slate such early states as Illinois, Pennsylvania and Florida, partly because of a lack of resources, partly because, as one observer noted, "he thought the power of his ideas, not organization and delegates, was what counted." As a result, Hart didn't get a single one of Pennsylvania's 195 convention delegates and only 41 of Illinois' 194.

Former vice president Walter F. Mondale edged Hart in the total popular vote in the 1984 Democratic primaries, 6.8 million to 6.5 million, but he won nearly twice as many delegates, 2,191 to 1,200.

"I think we lost it because we were campaigning to win small state primaries instead of slating delegates," said Kathy Bushkin, Hart's 1984 campaign press secretary. "We were campaigning in Idaho, but Mondale was calling delegates in Ohio."

Rick Ridder was one of Hart's chief delegate hunters.

"We didn't even know the early filing deadlines until December of '83, when we were broke and at the low point of our resources," Ridder said. "We couldn't find people to be delegates and there was a cold spell, which kept people off the street. In Pennsylvania only about 5 percent knew who he was and Florida was a disaster. No one knew who he was.

"You can't start too early. It's a monumental process."

The organizational problem is even worse this year because the primary and caucus schedule is far more crowded early on -- "front-loaded" -- because of the "Super Tuesday" southern regional primary on March 8. About half the states will have held their primaries or caucuses before March 15.

This means the stakes also are larger because about half the committed delegates of both parties will have been chosen.

On the Republican side, which has a number of winner-take-all primaries in some states, including Texas and Florida, a candidate who wins a string of victories in February and early March can score a quick knockout, if he has qualified slates of convention delegates in those states. On the Democratic side, where delegate allocation is proportional to the candidate's popular vote, each candidate has a chance of remaining alive if he does well enough in the early primary votes and has qualified delegates.

The early deadlines and complexity of the delegate slating process in Illinois and Pennsylvania, and to a lesser extent in New York, are relics of the processes the bosses of the old political machines devised to exclude outsiders. The southern states' rules generally are less convoluted because most have recently converted to primaries from caucuses, which were their traditional means of exclusion.

Despite the complexity, all the candidates of both parties, except Republicans Haig and former Delaware governor Pierre S. (Pete) du Pont IV, are aiming for full slates in all states. This includes Hart, despite his reentry into the race less than a month ago.

"So far we've met every deadline and we think we'll meet the rest," said Sue Casey, Hart's campaign manager.

One reason Illinois and Pennsylvania are so difficult is that they are "unforgiving." This means that if the candidates don't meet all the requirements on deadline they don't get their delegates. In most other states there are provisions for adding convention delegates after the primary. Among the states:

Illinois. The candidates had to file petitions bearing the valid signatures of 3,000 registered voters last Dec. 28 to get their names on the primary ballot.

Today, they have to file the names of delegate candidates, allocated among each of the 22 congressional districts (the better the party's vote in the previous election, the more delegates the district gets). In addition, they have to file petitions bearing as many as 1,000 signatures for each congressional district's delegate slate, also weighted for the previous vote. If a candidate's petition is short of valid signatures, he loses his delegate slate in that district.

Pennsylvania. Delegate candidates for each of the 23 congressional districts had to submit their names by Jan 5. Each delegate candidate must get 250 valid signatures in his or her district by Feb. 16, the day of the New Hampshire primary.

Illinois and Pennsylvania -- as well as New Jersey, whose primary is in June -- are "loophole" or winner-take-all states in which it is possible for a candidate to sweep a congressional district and win all its delegates -- and win every district and all the state's convention delegates.

New York. The candidates must file the names of delegate candidates allotted to the 34 congressional districts by Jan. 20 and 10,000 signatures statewide to get on the ballot. Between Jan. 26 and Feb. 26 the Democratic candidates need to get 1,000 valid signatures, the Republicans 1,250, for each congressional district slate.

Texas. Republican presidential candidates need 5,000 signatures statewide, not allocated by congressional district, but with each signature including the voter's registration number to get the candidate's name on the ballot. If any of the GOP candidates' petitions fall short after the party audit, they will win no Texas delegates regardless of how they do in the popular vote.

Democratic presidential candidates have the option of paying a $5,000 filing fee instead to get on the ballot, and all but Jesse L. Jackson exercised the option.