RONALD REAGAN will probably be getting the bill for the small government plane that flew Nancy Reagan to New York on a shopping expedition Tuesday.

But even if he gets stuck with the bill personally, it was a bargain.

The White House military affairs office, which arranged for the flight, figures the cost to the government at $389 an hour for a C-12 turbo-prop.

Originally, Mrs. Reagan had intended to take a Jet Star until she found out they cost $1,613 an hour. She opted for a slower, cheaper plane.

The two-hour round trip of flying time ended up costing about $778.

Since Mrs. Reagan was accompanied by two Secret Service agents, the Secret Service gets billed for a proportionate amount.

Normally, a spokesman said yesterday, the Secret Service pays "the equivalent of a first-class seat."

Calculated that way, each agent would pay $198, or $396, leaving Mrs. Reagan's share at $382, which isn't much considering the luxury and comfort involved.

Her bill, according to the White House press office, is being forwarded to the Reagan transition team. But no one could be found there yesterday who knew what arrangements were being made for payment.

Vernon Orr, who is the Reagan transition office's assistant director for administration, said he had not authorized the ticket and didn't even know Mrs. Reagan was in New York.

The transition team has a $2 million budget from the federal government. But that money isn't supposed to be used for personal expenses. The families of presidents and presidents-elect are supposed to reimburse the government when they travel on military aircraft on unofficial trips.

That means it is probably going to cost Ronald Reagan $382 for this week's trip.

It will be cheaper after he takes office.

At that point, his family members get billed the same way as the Secret Service for the equivalent of first class fare plus $1.

A White House spokesman said yesterday that Rosalynn Carter had used for personal business a small military aircraft only once in four years that anyone could recall.

She used a Jet Star to attend the funeral of a family friend.

Mrs. Carter flew to New York to shop on one occasion the entire time she was the first lady, another aide said. That was early in 1977, and she flew commercial.

From then on, things were brought down from New York to the White House for her to make her selections.