Television evangelist Marion G. (Pat) Robertson is using a claim of tax deductibility to help raise millions of dollars for an organization that is financing the mobilization of Christian evangelicals who could form his base of support should be decide to run for the presidency.

Robertson's Freedom Council, in its newsletter and political materials, has told potential donors their contributions are tax deductible, but the Internal Revenue Service has not yet ruled on the tax status.

Also at issue in Robertson's fund-raising methods is his contention that council use of contributions to mobilize voters is an educational activity, not the partisan political activity of the type that would be covered by federal campaign regulations. Several of the other potential 1988 presidential candidates have political action committees governed by state and federal election laws.

Robertson's Freedom Council played a central role in his strong showing last week in the preliminary stage of the Michigan Republican primary, an early test of strength in the 1988 presidential nomination process. Nationwide, the council expects to spend $4 million encouraging fundamentalist Christians to participate in politics this year. In Michigan, the council has spent more than $300,000.

Robertson says the council qualifies as tax deductible because it is nonpartisan, encouraging Christian participation in both major parties.

It "is not political money, that is educational money," Robertson said at a news conference May 16 before a fund-raising dinner at which donors gave as much as $20,000 a couple to the Freedom Council. "We have done work to get people who care about traditional values into the political process, but we have to do it on a nonpartisan basis."

In Michigan, the council set up a political organization with 14 staff members, including nine assigned responsibility to recruit precinct delegate candidates for the Aug. 5 primary. That primary is an early step in the process that will select Michigan's 1988 GOP convention delegates.

As part of the recruitment effort, the council held a $90,000 rally on May 8 in Detroit, televised by satellite to at least 15 other Michigan locations. The gathering looked like a traditional political rally for Robertson. He told the group of 3,000 to 4,000 cheering supporters that "Michigan will become the first state in America in 1986 to be saying who the Republican candidate for the president of the United States should be . . . . Christians in Michigan can say we stand for values, we stand for family, we stand for God and country, we stand for liberty and freedom."

At the end of the rally, a questioner asked Robertson about his 1988 plans. He replied, "Thousands of people have been asking me to get involved, to be a candidate for president of the United States . . . I am crystallizing a decision, so let me ask you here in Michigan, should I do it?" The audience then roared "yes."

Freedom Council literature passed out at the rally told prospective precinct delegates they could choose either party. Officials of the council said 4,900 supporters filed as Republicans and 500 to 600 filed as Democrats.

Two former IRS commissioners, Sheldon Cohen and Jerome Kurtz, in interviews questioned the legitimacy of tax-deductibility claims by organizations actively involved in a primary election. Neither former commissioner would comment specifically about the Freedom Council, but both noted that the law is designed to provide tax benefits only for charitable activities, not politics.

Political activity by a charitable organization, Cohen said, is "pushing it the law to the outer edges. The question is what the law was designed to do, and the answer in the case of political activity is clearly no."

"As an abstract proposition, a charity that gets involved in campaigning of any kind is getting in trouble," Kurtz said.

He cited provisions barring tax-deductible charities from "carrying on propaganda or otherwise attempting to influence legislation . . . including the publishing or distributing of statements supporting any political campaign on behalf of any candidate for public office."

The council's newsletter, the Freedom Report, declares that donor "contributions are now tax deductible." The newsletter adds, "We expect official approval shortly."

Similarly, material handed out in Michigan asked donors to declare:

"Yes, Pat! I will try to become a delegate in my precinct. Yes, Pat! Have someone contact me from the Freedom Council. I want to volunteer. Yes, Pat! I want to help pay for Operation Michigan. Enclosed is my one time gift . . . All gifts are fully tax deductible. Make checks payable to: The Freedom Council."

Robert Skolrood, general counsel to the National Legal Foundation, an affiliate of the council, said he was not aware that Robertson had claimed tax-deductible status for the Freedom Council. "In my opinion, it should not be done until you get the tax status," he said.

Johnell Hunter, who handles inquiries for the IRS, said an organization "cannot say donations are tax deductible until they get their new tax status." Anyone claiming a deduction for a contribution to an organization without the special tax status would have the deduction disallowed, she said.

The undecided tax status of the Freedom Council has other ramifications. Dick Minard, the council's national director, said half of the council budget comes from individual and corporate contributions, and the rest, about $250,000 a month, is given directly by the Christian Broadcasting Network (CBN), Robertson's television network, which does have tax-deductible status.

According to Steven Payek, a spokesman for the IRS, and former IRS commissioners Kurtz and Cohen, a failure by the council to qualify for tax-deductibility status would raise potentially significant problems for CBN.

Cohen said a charity cannot give money to another organization which then uses the cash for non-charitable activities. For a charity to give money to a political organization would amount to channeling contributions given special tax status by the federal government into the political area, Cohen, Kurtz and Payek each separately pointed out.

Other prospective presidential candidates, including Sen. Gary Hart (D-Colo.) and Rep. Jack Kemp (R-N.Y.), have set up tax-deductible "think-tank" foundations. Only Robertson, head of CBN, is using supposedly tax-deductible money to finance voter mobilization activities.

Vice President Bush and Kemp are financing their activities with nondeductible contributions. Bush uses his Fund for America's Future, which publicly reports receipts and expenditures. Kemp backers use the Michigan Opportunity Society (MOS), which has not disclosed contributors.

MOS officials claim that contributions meet federal requirements: a ceiling of $5,000 on individual donations, and a prohibition against corporate money. Robertson says the Freedom Council can accept money from corporations.