When the Reagan administration launched its drive to sell millions of acres of federal land, it announced it would seek the help of the nation's real estate agents to get the effort moving.

Now, nearly a year later, there's a difference of opinion over what role the real estate industry should play and how much their help is needed now.

The White House's Property Review Board, which is pressing agencies to clear their properties for sale, wants to involve the agents almost immediately, while the General Services Administration, which has been selling federal property for decades, thinks it can manage without them.

Joshua A. Muss, executive director of the review board, told the National Association of Realtors' convention recently: "Realtors are helping us to identify excess federal property that could be put to better use . . . and we are going to call on their expertise and knowledge to help us develop marketing strategies for these properties."

Muss said recently that he had the impression that GSA had in place "a new marketing plan that immediately put brokers to use." While GSA officials said that plan exists, they contend they can handle the program without the help of the real estate agents, at least for the time being.

Earl E. Jones, GSA's assistant commissioner for real property, said an increased budget in fiscal 1983 will allow him to hire GSA realty specialists in three waves, as needed, over the next six months.

Brokers will be used, he said, "as a last resort, when we can no longer hire people to handle the sales and when we have an overwhelming amount of property in our inventory."

GSA spokesman Paul W. Costello said that the long-range plan is to use brokers for about half the sales.

"Eventually, we will get to the point where there is no way we could handle it all," Jones said. "If it all comes in as expected, we'll have to turn to Realtors to help."

GSA has 577 properties on its inventory of surplus properties, but not all of them have been cleared for sale. The administration's plans call for the sales program to raise $17 billion over five years. This year, GSA has a sales target of $1.2 billion.

Past and present GSA officials, however, have expressed concern over whether the agency can legally pay the real estate agents commissions for identifying and marketing properties without awarding them contracts to perform specific jobs.

The Realtors' trade group has established a program called AID (assist the inventory and disposal), which involves identifying and marketing surplus federal property. Jones declined to comment about the plan.

But Roy Markon, former head of GSA's Federal Property Resources Service, said, "They just can't do it that way. It's not legal. There's no place in the law for Realtors to get a commission for identifying or marketing property unless they are under contract with the government." Muss' response is that the agency can find a way to do it if it wants to.

Thane A. Young, director of energy and environmental affairs for the Realtors, said the group is offering to help because "the federal government has been selling property all along, but they haven't been doing it in an enterprising fashion."

Young recognizes that commissions may be "down the road." In the meantime, he said, "our people have been in contact with regional [GSA] administrators to become familiar with what properties are for sale."

"Agencies are not going to always be willing to identify all the property that they have that could be sold," Young said. "Nobody knows the real estate market like a Realtor in a particular locale."

While GSA has had the authority since 1949 to use real estate agents for specific sales, it has used them only on rare occasions and not at all in the past three years.

At this time, GSA plans to invite brokers to bid for the right to sell only one property: 1,200 units of vacant military housing an old base in Glasgow, Mont. GSA recognizes that there is no local demand for the property, so it wants to find a real estate broker who will look for a buyer nationwide.