When Congress takes a break between sessions, some members continue working. They work on their tans. They work on their wardrobes. They work on their snorkeling skills. Anything to serve the American taxpayer. For the American taxpayer, after all, picks up the tab when members of Congress go abroad on ''official business.''

Funny how much official business crops up in the tropics every winter. During the recent congressional recess, dozens of lawmakers clambered aboard military jets with their spouses and staffs. Most of them headed for warmer climes.

We tracked the records of 74 members of Congress who traveled through 34 countries on ''official business'' in January. One would think we were negotiating world peace with Australia or New Zealand. Twenty of the members managed to include those two countries on their list of official visits in January. A staffer at the New Zealand Embassy in Washington explained the attraction: ''Our January is like your summer vacation.'' Other popular destinations included New Guinea, Thailand, Taiwan and Tahiti.

While many of the January junkets examined by our associate Jim Lynch had the appearance of thinly disguised vacations, congressional travel abroad receives little, if any, scrutiny. Nobody will challenge, for example, the merits of a recent three-day, expense-paid visit by a House committee to Ecuador's tropical Gala'pagos Islands.

No oversight committee decides whether the junkets are legitimate government expenses or simple pleasure trips. Junkets are usually authorized and policed at the committee level by the same junket junkies who arrange and take them. The operative motto is: ''Join Congress and see the world.''

We questioned spokesmen for both the House and Senate ethics committees, and they could not recall any investigations into alleged abuses of the foreign travel privileges. Bonnie Parker, staff administrator of the Senate Ethics Committee, bristled at the hint of impropriety. ''You never see such reports of that on the Senate side,'' she said. Parker explained that senators avoid the nouveau tackiness of junkets because ''they are older and more experienced'' than politicians in the House.

It must have been serious business, then, that took five senators and their wives through Australia, New Zealand, Korea and the Philippines in January. The delegation, headed by Sen. James Exon, spent $209,000 just on the cost of flying on an Army C-135 jet.

A glance inside January's junket records revealed that officials in the foreign countries visited by our legislators often were not available for meetings. Maybe someone forgot to call ahead for an appointment. Entire days for the U.S. delegations were devoted to shopping, swimming and snorkeling.

One delegation, led by Rep. Don Edwards, spent a three-day stretch in Peru during which the only official activities noted on the agenda sent to the State Department were ''acclimatization to the altitude'' and tours of the ruins.

The Congressional Budget Office has no estimate of how much the government spends flying members of Congress around the world. Neither do the appropriations offices of both houses of Congress. Domestic travel comes out of each committee's spending pot, but foreign travel expenses spew from a ''permanent indefinite appropriation fund,'' explained one appropriations official.

If the past rate of spending is any indication, junketeers look permanently, indefinitely out of control. Between January 1984 and September 1985, Congress spent $9.2 million on junkets, according to Congress Watch, a nonprofit group affiliated with consumer advocate Ralph Nader.

Our review of January's junkets indicates that the numbers are likely rising. Nearly all of the Congress members and their staffs who travel abroad now get not only free transportation and a healthy per diem but also an all-time high of $50 a day in ''subsistence allowance.''

And subsistence is tough, considering the destinations. Five of the 23 delegations we studied managed to squeeze Honolulu into their rigorous schedules. On the beaches of Waikiki, they presumably contemplated the shifting panorama of rising and falling national issues.