Conservative senators led by Jesse Helms (R-N.C.) who have put a "hold" on 29 presidential appointments to State Department posts have infuriated the department and many of their colleagues, but according to sources in the Senate and at State, little can or will be done besides waiting them out.

That is in part because delaying confirmations is a custom as old as Congress, and in part because trying to change it would mean taking on Helms, the Senate's champion pusher of the "hold" button.

Helms is leading a group of nine conservative senators who want six ambassadors and Foreign Service employes "taken care of" with new or continuing jobs as a condition for allowing the Senate to consider the 29 nominees.

In a letter to Senate Majority Leader Robert J. Dole (R-Kan.) last week, Helms delivered in writing the kind of specific demand usually only suggested in private: that one of the six threatened conservatives should be named ambassador to either Panama or Belize. White House chief of staff Donald T. Regan came up with jobs for only three of the six, not including the requested ambassadorship, and the hold continues.

Dole is not amused. "This is just a struggle between some Republican senators and the secretary of state," he said last week.

A top State Department official agreed, but refused to utter a word of criticism for publication. "These are very powerful people. We don't want to knock their noses out of joint," he said.

A top Senate staff aide said Helms' power comes in part from his influence over conservatives nationwide, who are likely to criticize or contribute to senators as Helms directs. Diplomats hoping for promotion also know that Helms can make any future confirmation a prolonged ordeal, the aide said.

Helms led the charge in 1981 for "a housecleaning in the Asia bureau," winning the replacement of two senior officials in return for lifting a five-month hold on John H. Holdridge as an assistant secretary. He also held up the assistant secretaries for Africa and Europe and the undersecretary for economic affairs in 1982, and later caused two of President Reagan's nominees to the Arms Control and Disarmament Agency to be withdrawn.

In a letter then, he said he wanted only to ensure that policymakers "reflect, to the fullest extent possible, the president's views."

Helms is famous for his avalanche of written questions to targeted nominees. Last week he submitted 150 of them to Thomas R. Pickering, former U.S. ambassador to El Salvador, as the Senate Foreign Relations Committee closed its hearing on Pickering's nomination to be ambassador to Israel. Helms indicated that, if the questions were answered by the next day's hearing at 11 a.m., Pickering might be confirmed that day.

A State Department source said five people worked until 4:30 a.m. writing up the answers. The questions ranged from how Salvadoran political parties finance themselves and the ideologies of all the Salvadoran guerrilla groups to the record of visa rejections for several Salvadorans.

But the hold was not lifted and Pickering remains in limbo.

Helms' strategy "is to make a lot of demands to get concessions," said Scott Cohen, former Senate Foreign Relations Committee staff director. "He doesn't expect to win them all, but if he breathes enough fire, the executive branch may yield here and there and he gets appointments for people he especially admires."

The first "hold" occurred in 1789, when the two Georgia senators objected to President George Washington's nominee for customs inspector at the port of Savannah, according to Donald A. Ritchie, associate Senate historian. Washington withdrew the nomination.

The idea grew that senators had the right to block the appointment of anyone they found "personally obnoxious" from or in their home states, Ritchie said.

Pat Holt, another former Foreign Relations Committee staff chief who retired in 1977 after a 27-year career, recounted an episode similar to the current situation.

Former senator William (Wild Bill) Langer (R-N.D.) "rather forcefully told President Harry S Truman that there would be no more ambassadors confirmed until he appointed one from North Dakota," Holt said. Truman obligingly named Thomas Whelan of North Dakota in 1949 as ambassador to Nicaragua, where he remained until well into the early '60s in the Kennedy administration.