Lt. Col. Oliver North collaborated with a conservative activist, Carl R. Channell, to wage a multimillion-dollar campaign this year to influence Congress and American opinion on behalf of the Nicaraguan contras, sources familiar with the campaign said.

The campaign, which came as the rebels were complaining that private fund-raising efforts had been disappointing, included lobbying in Congress for the Reagan administration's $100 million contra aid request, financial support for the rebels' main Washington office and an aggressive television ad campaign portraying the contras' congressional opponents as Communist dupes.

Sources familiar with the campaign said North provided Channell's media consultants with information on contra aid in Central America to help them portray U.S. policy in the region.

It is illegal under federal law for an active-duty military officer or any other government employee to engage in partisan politics, a Defense Department spokesman said.

For his efforts, North presented Channell with a "Freedom Fighter" award at a black-tie dinner at Washington's Willard Hotel Nov. 11. Just two weeks later, North was fired from his White House post for allegedly engineering the diversion of funds from secret Iranian arms deals to the contras.

The whereabouts of the $10 million to $30 million North allegedly diverted remains a mystery.

Channell, 41, a former member of the National Conservative Political Action Committee, told reporters earlier this year that he had raised $7 million for television spots and said that his funds had come from "13 to 15" phone calls to wealthy Americans sympathetic to the contras.

But sources who claim to have knowledge of several of Channell's transactions expressed doubts Wednesday that Channell had raised the millions through conventional fund-raising. Contra leaders have said recently that they were experiencing severe financial difficulties and had found private fund-raising efforts this year extremely disappointing.

Last month when news of North's diversion of the Iran funds first emerged, contra leader Adolfo Calero estimated to reporters that private donations to the contras in 1986 had amounted to "less than $1 million." Channell, however, is known to have access to generous conservative donors.

Channell did not return phone calls placed both to his office at the Washington-based Endowment for the Preservation of Liberty and to the office of his lawyer, J. Curtis Herge of McLean, Va. Herge is active in establishing a legal defense fund for North.

Richard R. Miller of International Business Communications, a public relations executive hired by Channell this year, said the questions raised about Channel's fund-raising were unfounded. Miller said Channell had raised all of the pro-contra campaign funds from conservative American contributors.

Channell hired Miller's firm earlier this year to set up and manage the main Washington office of the primary contra umbrella group, United Nicaraguan Opposition (UNO), sources familiar with UNO's operations said. They said Channell's funds paid Miller's firm to choose and rent an office, staff it with clerical help, and cover phone and other expenses.

UNO's Washington office serves to promote the contras' point of view to reporters, members of Congress and the American public.

Channell also paid the salaries of some of the UNO representatives at the Washington office, the sources said. The sources estimated the rebels' monthly salaries at between $2,000 and $2,500 per representative.