Arthur M. Kuhl, who is in charge of the $45,000 appropriated for trips by American congressmen to meetings of the Interparliamentary Union, paused in the lobby of the Ritz Hotel here today, did a little arithmetic in his head and concluded that "we'll probably have to go back for a supplemental appropriation this year."

The expense vouchers from this 12-day trip to England, France, Switzerland and Portugal will scarcely have time to clear before it will be time for the next meeting of the IPU, in Vienna in May.

Kuhl, who is assistant to the secretary of the Senate back home, is executive secretary of the U.S. delegation to the IPU, whose gatherings are so ambient that delegates have gradually expanded them from annually, beginning in 1889, to a record three for this year. The third session is scheduled for Bonn in September.

Kuhl has managed to keep his cool under the demanding pressure of a 46-member party that includes four senators and 10 House members, largely because he has had so much help.

In addition to the traveling party, which includes a doctor and a military crew, which helps tote baggage, Kuhl has the resources of the U.S. Embassy here.

"I turned myself over to the embassy and said take it from here, said Kuhl, who is making his first trip to the IPU, an organization of legislators from 75 nations that discusses world problems.

The embassy responded by assigning 22 employes to operation CODEL (congressional delegation) IPU.

Mission headquarters is a suite of rooms of the third floor of the Riz. The American deldgation occupies all of the 28 bedrooms on the third floor, with the four senators pulling rank by getting larger rooms than the representatives.

At $28 to $35 a night, the cost of the rooms alone, plus similar ones in Paris and London, more than $10,000 of Kuhl's $45,000-bydget, will be gone even with the 20 percent Embassy Discount accorded the delegation.

Kuhl said the annual appropriation has not been increased in several years, and what with inflation and a third conclave, he's certain it will not stretch.

The $45,000 does not begin to cover the actual cost of the trips, because much of the expense is charged to another federal agency, such as transportation to the Department of Defense, and embassy costs to the State Department.

The vew of the Air Force jet that is ferrying the delegation around numbers 22, including seven security officers who guard the plane around-the-clock.

The embassy's contribution includes providing 10 cars and drivers, and one bus and driver, that are being used to carry the delegates back and forth from the hotel to the convention center, where IPU meetings are being held, as well as to the embassy, and for shopping and sightseeing trips along the Portuguese coast.

No detail has been overlooked.

The embassy suite includes a check-cashing and money-changing desk, signup sheets for shopping and sight-seeing excursions, and an English-language instruction sheet on how to gamble at the Casino Estoril.

Not every request can be granted, no matter how extensive the effort. Tuesday afternoon, for instance, Sen. William L. Scott (R-Va.) told the embassy staff that he and his wife, Inez, wanted to go shopping between 1 p.m. and 3 p.m.

Scott was told that nearly all stores in Lisbon are closed for lunch during that time. But Scott was so insistent he go at that time that the Portuguese woman assigned by the embassy to escort the Scotts was nearly in tears trying to find a shop that was open.

Scott showed his appreciation for the special attention yesterday by dropping off at the suite several picture books of Capitol Hill and an autographed Senate calendar.

Secretaries are on call in the event members of the delegation have any papers to be typed, and the room is staffed from 7:30 a.m. until at least 10:30 p.m.

An embassy employe has been assigned to coordinate each major social event on the IPU schedule, including tonight's special performance of the National Ballet at the Sao Luis Opera House.

The suite has become the focal point of activities and tonight it was the scene of a suprise party for Rep. Robert McClory (R-Ill.) and his wife, Doris, who were celebrating their ninth wedding anniversary.

Sen. John Sparkman (D-Ala.), chairman of the delegation, recalled that the McClorys attended their first IPU conference in Vienna in 1969, shortly after their marriage.

The physician who is accompanying the delegation, Army Col. Robert Holmes, came in handy in Paris over the weekend when the wife of Kuhl's boss fell on a wet cathedral step.

Eunice Kimmitt, wife of the secretary of the Senate, J. Stanley Kimmit, suffered a broken left arm and knee cap.

Holmes examined Mrs. Kimmitt in his room at the Hotel Crillon and quickly called an ambulance.

"I make if a policyt o locate a hospital when I arrive in a city," Holmes said, "just in case I have to find one in the middle of the night." In Paris, he had selected the American Hospital, and Kimmitt was admitted.

A French orthopedic surgeon recommended that surgery be performed on both her knee and arm "and we elected to send her home," Holmes said.

Kimmitt and her husband returned to Washington today, aboard a regularly scheduled Air Force "Nightingale" flight that interrupted its regular trip from Madrid to Frankfurt to pick up the kimmitts in Paris.

The Air Force has to flights a week from Frankfurt that carry "medical evacuees" from hospitals throughout Europe, mostly military personnel, who are being transferred to stateside hospitals.

Holmes said that because the French physician said the surgery should be performed within 72 hours, "I didn't feel justified in getting a Mission Scrambled (special flight) for her."

Since the group arrived in Lisbon on Monday, Holmes' practice has been limited to passing out Aspirin, and Bandaids, and cautioning members of the delegation to "take it easy. They go at an incredible pace on these trips," said Holmes, who is making his fourth or fifth congressional trip. Holmes is an internist at a Fort Myer, Va. clinic.

Col. Joseph Maupon is the military escort, and he has made so many of these trips that he stopped counting a long time ago, "especially those to Panama."

Maupin said he accompanied Sen. Soctt, one of the Senate's premiere junketeers, on a trip to South America last August "that The Post raised such a fuss about."

Maupin is the chief of a five-member military detachment (plus the aircraft crew) that stands ready to act whenever "someone puts a requirement on me."