Sen. Jesse Helms (R-N.C.) is widely suspected by State Department professionals of trying to impose his conservative views on the Foreign Service by blocking the ambassadorial nominations of career diplomats whom he suspects of liberalism.

His latest targets have been Richard Viets, named as ambassador to Portugal, Nicholas Platt (Philippines) and Melissa Wells (Mozambique). The senator's attempt to block their approval by the Foreign Relations Committee moved George Vest, director general of the Foreign Service, to an unusual expression of displeasure toward a powerful senator.

All three career diplomats have "top-notch" credentials, Vest told our reporter Daniel Kaufman. "If a person has a long and very well-known and distinguished career," Vest said, "you have one {Senate} hearing only, because life in the Foreign Service is an open book. In each of these cases, more than one hearing was called for at the instigation of Helms."

Helms' spokesman, Tom Boney, denied that the senator is "out to get" anyone in the Foreign Service, as critics have charged. Boney said Helms is just examining each nomination thoroughly "on an individual basis."

In the case of Viets, at least, Helms appears not to have based his objections on ideological grounds, but on questions about financial practices during Viets four-year tenure as ambassador to Jordan. The questions were first raised in 1983 by the State Department's inspector general.

A memorandum Helms sent to his committee colleagues takes issue with Viets sworn testimony on the financial questions:"Overt terrorist threats" and "substantially modified" regulations exempted Viets from having to pay for his family's use of government vehicles in Amman, the former ambassador contended. Helms said Viets is required to repay the government at the rate of 20.5 cents a mile.Viets explained a substantial "loan" from an embassy employe by saying he merely "kept it for her" as a longtime friend so it would earn interest in his bank account. Helms pointed out that the ambassador's 1984 financial disclosure did not show a sum that large in any of his bank accounts."Extraordinarily high liquor consumption claims" -- in Helms' phrase -- were explained by Viets as gifts for Jordanian guests, their security guards and drivers. But Helms complained that Viets offered no evidence to justify his claim for reimbursement on the liquor bills.

When the committee approved Viets' nomination, 12 to 5, liberal Democrats Alan Cranston (Calif.) and Christopher J. Dodd (Conn.) joined Helms and two other Republicans in voting against approval. Chairman Claiborne Pell (D-R.I.) acknowledged that "a number of irregularities were raised" about Viets, but said the nominee had not shown "intentional disregard of either law or regulation," and added: "The committee does not believe that one adverse audit report in an otherwise long and distinguished career should be the basis for the rejection of this nomination."

Viets said he would not comment until the full Senate votes on his nomination.