Gale McGee, President Carter's choice for ambassador to the Organization of American States, reflected yesterday on his new financial status.

He is enjoying, he said, "a luxury I never had before."

That "luxury" is a $120,464 surplus from his unsuccessful campaign for re-election t to the U.S. Senate last year. He can use it to mount another political campaign in months or years hence, which he well may do. Or he can simply put it in his pocket for any use he chooses.

That option is perfectly permissible under the federal election laws, which provide that surplus campaign money can be used for "any . . . lawful purpose."

It is roughly the same provision that has permitted House Majority Leader Jim Wright (D-Tex.) to use political funds to pay off personal debts and taxes.

Pending McGee's decision on what to do with the money, William G. Dell Sr., who heads McGee's campaign committee, has invested $75,000 in high-interest certificates of deposit, a portion of the balance is short-term notes, and the rest I, kept in cash.

McGee said the cash is there to pay for possible immediate political expenditures, "such as going to Wyoming to prowl around. I want to keep that option open."

The Wyoming Senate seat now held by Republican Clifford P. Hansen is up next year and added McGee, "the governor's spot, too; you never know what may happen."

McGee said his new OAS position has been interesting so far and so "I change about every other night" on his plans for the future.

Dell said the committee would pay taxes on the interest income drawn this year by the fund "until [McGee] makes up his mind."

After his defeat, McGee met with lawyers from the Federal Election Commission to discuss what could be done with his campaign surplus.

According to treasurer Dell, surplus money used for political purposes must be accounted for.

"Any amount can be converted to McGee's personal use" if he pays taxes on it as income, Dell added.

Dell also said the former senator could convert the entire $120,464 to his own use if he decided in the future he would not run - as long as he paid the income taxes. That has been a common, but little-publicized congressional practice in past years.

McGee said yesterday, however, that "I haven't gone any further" than planning possible use of the funds for future political campaign.