PAINTING THE contras as "the moral equivalent of the Founding Fathers," as President Reagan once did, has always taken exceptionally heavy brushwork. It will take more if the Democrats have their way.

Sen. John Kerry (D-Mass.) has been quietly pursuing allegations of drug-trafficking, skimming of money and other illegal activities among the spiritual descendants of the folks at Valley Forge. Kerry was opposed to contra aid before any of these matters were brought to him. But he regards them of sufficient gravity and substance as to merit the attention of the Senate and a public hearing.

Richard Lugar (R-Ind.), chairman of the Senate Foreign Relations Committee, Reagan loyalist and contra supporter, is a reluctant dragon in this matter. His eyes do not light up with investigative zeal. But he has promised Kerry out of senatorial courtesy that his staff will cooperate with Kerry's in looking into the allegations.

Lugar has been one of an earnest little band of moderate Republicans and conservative Democrats who have been pressing reform on the contra leadership. He is trying to instill in them some understanding of human rights, civil rights and other basics of democracy -- "the things," he says ruefully, "we accuse the Sandinistas of taking away."

He says that hearings might be held before June 9, the date set for yet another vote on contra aid in the House, where it has been hotly contested.

Accusations of corruption among the "Freedom Fighters" have been floating around Washington for months now. Even Elliott Abrams, assistant secretary of state for inter-American affairs, has acknowledged troublesome charges of drug-smuggling, but he insists it stops short of the leadership.

One of the most vociferous advocates of finding the facts is Rep. Charles Stenholm (D-Tex.), an unshakable friend of the contras. Stenholm was advised of skulduggery by a rich right-wing Texan named Phil Mabry, a heavy contributor to the cause. Mabry complained in a National Public Radio broadcast that he told the contras and their White House confederates to clean up their house -- and "for some reason or other, they didn't."

The Justice Department has been probing, too, but an unnamed official told the New York Times that "there just ain't any evidence." The anonymous spokesman called the charges "pure politics."

Some House Democrats, with one eye on Lugar's reluctance and the other on the calendar, hope to launch an investigation of their own. A delegation of liberals, including David Bonior (Mich.), Don Edwards (Calif.), David Obey (Wis.) and Norman Mineta (Calilf.) called on Speaker Tip O'Neill and Whip Thomas Foley (Wash.) to push for a full-scale probe, ideally headed by Judiciary Committee Chairman Peter Rodino (N.J.), of Nixon impeachment distinction. Subpena powers and a large staff of investigators will be needed to insure that the effort cannot be dismissed as merely partisan.

None of the powwow participants demurred on the need to go forward. The only caution sounded was that care must be taken with the material. So many flakes and felons and rogues are involved that one of them could by bring down the whole investigation.

Rodino has already assigned some questions to Rep. William Hughes (D-N.J.), chairman of the House Judiciary subcommittee on crime . Hughes is currently looking into the bizarre case of the two Nicaraguan drug-smugglers who were convicted of importing $100 million worth of cocaine to California.

In the weirdest development in the case, the government gave back $36,000 of the haul to one of the defendants, Julio Zavala -- allegedly after he had presented letters from contra leaders attesting that it was really "political money, for the reinstatement of democracy in Nicaragua."

Kerry will not discuss any specifics, wanting to proceed in the name of the Senate. Lugar is having his staff work with Kerry's people to sift out the allegations. He is drawing up a witness list he hopes will be "balanced" and lining up administration people for the defense. Such matters as a supposed conspiracy on the part of rival contras to kill Eden Pastora, the presence in the contra high command of a man alleged to be connected to the murder of Archbishop Romero, the disappearance of $15 million in funds sent for humanitarian aid and illegal arms shipments could be aired.

No matter what comes out, the public will not be swayed one way or the other. The public is at 2-to-1 against contra aid and holding. But members of Congress who groan and writhe as every contra vote comes along might begin to look at the situation differently.

If it turns out that the contras are gangsters, some senators and congressmen might be freed of their present terror of being accused of "losing Nicaragua." Pushing "drugs for democracy" is not, after all, the American way.