Citing evidence from three 1980 Senate campaigns and the recent statements of a top White House political aide, leading Democrats yesterday demanded a Federal Election Commission investigation of the "independence" of the National Conservative Political Action Committee (NCPAC).

Rep. Tony Coelho of California, chairman of the Democratic Congressional Campaign Committee, said his group, the Democratic Senatorial Campaign Committee and the Democratic National Committee would file a complaint alleging collusion between NCPAC and Republican candidates and campaign officials.

"If we don't get action from the FEC," Coelho said, "we intend to pursue it in court and take it all the way up."

The Democrats acted on the basis of a legal memo from Robert F. Bauer, counsel to their Senate campaign group, citing results of a lengthy study of alleged collusion in last year's Iowa, Missouri and South Dakota Senate races.

The memo alleges NCPAC, which spent a total of $432,196 in the three states, helped recruit candidates, directly supplied them poll results, helped them raise money, and supplied them campaign workers and advice.

In Iowa, for example, where NCPAC waged an "independent expenditure" campaign against former Democratic senator John Culver, the memo charges that NCPAC sent out an emotional fund-raising letter that asked people to send money to Sen. Charles E. Grassley's campaign headquarters.

Bauer also cited "additional and compelling evidence of NCPAC's collusion with the Republican Party in making independent expenditures" in the statements made last Monday by Edward J. Rollins, now the deputy assistant to the president for political affairs who will succeed Lyn Nofziger as the top White House political operative in January.

Rollins was quoted by The Washington Post as telling a group of reporters, in reference to NCPAC and similar conservative political-action groups, "Very clearly we will be meeting with them regularly, to tell them where we're heading and let them tell us what they're doing."

Rollins said in the same interview that he understood NCPAC could not "coordinate" its activities with those of the White House and the GOP campaign committees without running afoul of the election law. But he said they could discuss "general strategies" and not specific races without jeopardizing the exemption that independent-expenditure groups enjoy from the overall campaign spending limits in the law.

Bauer's memo contended that was a misreading of the law, and Coelho contended that the Supreme Court, in approving the independent-expenditure exemption, "never intended this kind of thing to happen."

Rollins yesterday disputed this. "As long as we're just talking about common goals--the election of conservative Republicans--there's no violation," he said.

"To date, there's never been any meeting where any individual race has been discussed with NCPAC or any similar group," he said. "The Democrats are clearly grasping at political straws."

In Missouri and South Dakota, as in Iowa, the Democrats allege there was evidence of collusion on specific candidacies. In South Dakota, the Democrats allege NCPAC supplied Sen. James Abdnor with polling data and helped persuade him to enter the race against former senator George McGovern. In Missouri, where NCPAC waged an unsuccessful campaign against Sen. Thomas F. Eagleton, Democrats allege there were close ties between NCPAC and campaign aides to Republican challenger Gene McNary.

Terry Dolan, NCPAC executive director, could not be reached for comment last night.