Three of the leading Republican presidential contenders, Ronald Reagan, John Connally and George Bush, have collected more than $600,000 in excessive contributions for their 1980 campaigns, according to a complaint filed yesterday with the Federal Election Commission.

The allegations were made by the National Committee for an Effective Congress, a liberal politcal fund-raising organization. Its spokesmen contended that the "political action committees" set up for each of the three Republicans before they announced their candidacies had been used as an illegal device to get around federal campaign-contribution limits.

Under federal election laws, individuals can contribute no more than $1,000 to a candidate during his or her entire campaign for nomination. The laws also permit maximum contributions of $5,000 each to "political action committees" set up to support more than one candidate.

Supporters of Reagan, Connally and Bush set up separate organizations over the past few years to finance pre-announcement speechmaking and publicity drives.

According to the NCEC, these organizations collected up to $5,000-sometimes more-from hundreds of individuals. The contributors then gave still more money to the formal campaign committees set up this year for Reagan, Bush and Connally.

In all, the NCEC said, 375 donors contributed more than $1,000 each to one of the three Republican contenders.

"The record proves that these pre-presidential committees and candidate committees are controlled by a single group of people," NCEC Executive Director Russell D. Hemenway declared at a press conference here.

"The law states that such committees are affiliated and subject to a single contribution limit," Hemenway maintained. "It is obvious that these committees were used to evade the $1,000 contribution limits, in clear violation of the law."

Spokesmen for the three GOP prospects reacted angrily to the complaint and vigorously denied breaking any laws. They argued that the pre-announcement "political action committees"-Connally's Citizens Forum, Bush's Fund for Limited Government and Reagan's Citizens for the Republic-helped support friendly candidates for local office around the country.

Hemenway disagreed, contending that refunds must be made to contributors who gave more than $1,000 to any of Reagan's, Bush's or Connally's organizations.

According to statistics compiled by the NCEC, 52 percent of the reported contributors to Bush's now inoperative Fund for Limited Government also gave money to his presidential campaign committee.

Similarly, the NCEC said, 54 percent of the individuals who contributed to Connally's Citizens Forum gave money to the Connally for President Committee, and 22 percent of the contributors to Reagan's Citizens for the Republic made additional donations to his formal presidential campaign committee.

Hemenway also said there was a substantial overlap between those who ran the three Republicans' "political action committees" and the people now running their presidential campaigns.

Although federal election laws have been among the most difficult to interpret, the FEC, in a previous opinion concerning another case, cited overlapping officers and overlapping contributors as criteria for determining the extent of affiliation.

Spokesmen for Reagan, Connally and Bush did not seriously dispute the notion that the "political action committees" were in large measure surrogates for the later-to-be-organized presidential campaign committees. But they denied that this conflicts with federal election laws.

Peter Teeley of the Bush campaign called the NCEC complaint "frivoous" and said "we fully expect it to be dismissed by the FEC."

The "allegations are erroneous and totally irresponsible," Winton Blount, Connally's campaign chairman, said in a statement.

Said Lyn Nofziger of the Reagan campaign: "We have always been very careful to make sure that whatever we do follows the letter of the federal election law. And we're confident that we have done so."

FEC officials had no comment.