The millions of dollars that Uncle Sam doles out to international organizations each year are supposed to be closely monitored by appropriate federal agencies. The supervision, however, isn't always as tight as it could be.

For some reason, U.S. officials are sometimes more concerned about kowtowing to the sensitivities of other countries than they are about seeing that the money the taxpayers put up - usually the lion's share of the organization's budget - is wisely and properly spent.

The timorous attitude of American officials toward the Pan American Health Organization is an example. The United States furnishes two-thirds of the international agency's $80-million annual budget, which is expended on health projects in 32 nations in the Western Hemisphere.

Employees have come to us with allegations that PAHO director Hector Acuna of Mexico engaged in boondoggling to ensure his reappointment to the $44,344-a-year post. U.S. officials who knew about it shied away from interference for fear of damaging U.S. relations with Mexico.

Acuna landed his job for a four-year term in 1974 as the handpicked candidate of Mexico's then-President Luis Echeverria. When Echeverria was succeeded in 1976 by Lopez Portillo, Acuna realized that he needed the support of the new administration if he expected to be renominated for a second term.

One thing he did to cement relations with the Portillo people was to funnel a check for $100,000 to the governor of the State of Mexico for equipment to outfit an ecological center. Although the project won't be completed until next summer, the check was mailed on Nov. 4, 1977.

Acuna acknowledged to our reporter Vicki Warren that the influential governor whose state won the $100,000 grant is a personal friend. He funded the project early, he said, so that the money would not have to be turned back at the end of the year. "It is standard practice at the end of the year," he said, "to advance money when it would mean a savings."

Sources within the Pan American Health Organization told us, however, that an itemized list of the equipment to be purchased with the $100,000 has never been drawn up. And formal authorization for the loan went unsigned for at least a month after the check was singed. A copy of the authorization didn't reach the organization's Washington headquarters until nearly five months later.

A veteran employee of the health organization termed the circumstances of the funding "highly irregular." In addition, a spokesman for Acuna confirmed that expenditures for the ecology center were already running $60,000 over the amount budgeted for the project. He hastily added that "this often happens."

Perhaps the most convincing evidence that Acuna was buying support with PAHO funds was a payment of $20,000 in April of this year. The check, signed by the director, was hand-delivered to Mexico. The recipient was a social-services fund. The president of the fund was the wife of President Portillo. There was no stipulation as to how the money should be spent, according to an internal source. Acuna's spokesman conceded that the money was hand delivered, but he insisted that "it is not unusual for money to be brought in person."

Disgruntled employees also recall that in March 1975, Acuna approved a 19-month fellowship grant to his son-in-law for study of business administration in the United States. It is rare, said our sources, for fellowships to be awarded to students outside the health field. Most grants, moreover, fund only a year of study.

Acuna's spokesman acknowledged that "on the average, most fellowships are not that long." He explained that while the director personally approved the grant, his son-in-law had been recommended for the scholarship by the Mexican government.

Officials of the Pan American Health Organization are also aware that Acuna drew payments from the Mexican government after taking his post with the international agency. "It is against the organization's constitution," one staff member protested angrily.

Acuna maintained the payments were for annual leave he had accrued as a Mexican government official. The payments weren't made, however, until two years after he had left the service.

Asked about the allegations against Acuna, U.S. officials sought refuge behind protocol. "It is not appropriate for us to be looking into this ourselves," said Marilyn Kefauver of the U.S. Public Health Service. It would not be "good form" for the United States to investigate the situation, according to the State Department's liaison man with the health organization, Robert Andrews.

Acuna's friends in the State Department brought pressure on the other member nations to "vote for Acuna" over rivals from Uruguay, Ecuador, Venezuela, Panama and Jamaica. They left no doubt as to which candidate the United States favored. "We don't always cast our vote previous to the election, only when we feel we have to take a leadership role," Andrews told us.

Footnote: The efforts succeeded. Acuna was named to his second four-year term last month.