Twenty-two U.S. ambassadors took the extraordinary step yesterday of endorsing Sen. Jesse Helms (R-N.C.) for reelection, praising him for "a strong, close relationship with the Reagan administration."

The 22, all appointed by President Reagan, are not career Foreign Service officers and are not subject to laws limiting participation in politics by federal employes. Most are conservatives, and some have come under fire for openly expressing conservative opinions.

Helms is in a tight battle with Democratic Gov. James B. Hunt.

Helms' campaign announced the endorsements, and the senator, a member of the Foreign Relations Committee, which confirms ambassadors, appeared at a news conference in Raleigh with two of those who endorsed him -- J. William Middendorf II, ambassador to the Organization of American States, and Lewis A. Tambs, ambassador to Colombia.

The list also includes Evan G. Galbraith, ambassador to France; John A. Gavin, Mexico; John Davis Lodge, Switzerland; Paul H. Robinson Jr., Canada; and Helene von Damm, Austria. Joining in the endorsement was former ambassador Faith Ryan Whittlesey, now a White House special assistant.

Von Damm is a former personal secretary to Reagan, and Gavin is a former movie actor. Many on the list are personal friends of the president.

The State Department immediately issued a statement indicating that Secretary of State George P. Shultz had cautioned the ambassadors about making the endorsement, but observing that they had the legal right to do so.

"The U.S. ambassadors who have endorsed Sen. Helms are among those who are not subject to the Hatch Act, and they have made their decision strictly on their own responsibility as individuals," the statement said. "The Department of State is not involved in any political campaign. Secretary Shultz has stressed to our ambassadors that they are full-time federal employes whose primary task is the timely and successful completion of their official duties.

"This is in conformance with the policy established by the White House and in accordance with longstanding tradition which has discouraged ambassadors from participation in partisan political campaigns. While it is not unlawful for noncareer ambassadors to engage in some forms of partisan political activities, the secretary reminded them that their first responsibility is to the nation and the execution of foreign policy."

Government sources said that the White House counsel's office issued guidelines to all ambassadors early in the political year about partisan political activities and that those guidelines were reiterated by Shultz as the election approached.

Helms, one of the strongest supporters of conservative causes around the world, often has gone far to the right of the administration in pursuing foreign policy. As chairman of the Western Hemisphere ubcommittee of the Foreign Relations Committee, he backed Argentina in the 1982 battles over the Falkland Islands and is a strong supporter of right-wing politician Roberto D'Aubuisson in El Salvador.

Middendorf acknowledged those differences yesterday in the Raleigh news conference, saying: "All of us sometimes within the family must have disagreements . . . . "

But he said Helms' views are "respected as much as anyone in Washington" and added that the senator has "a strong, close relationship with the Reagan administration." Middendorf said the differences amount to "just two or three out of hundreds of times when he cooperated and supported [us]."

Claude Allen, a spokesman for the Helms for Senate Committee, said the ambassadors issued "individual endorsements."

The Helms campaign statement said: "Today, in an historic event, 23 U.S. ambassadors representing President Reagan and America around the world endorsed Sen. Jesse Helms for reelection. The ambassadors are all appointees of President Reagan and are on the front line of the president's foreign policy. The endorsements are a tribute to Sen. Helms' strong leadership role in strengthening America's foreign policy."

Other ambassadors endorsing Helms were:

David Abshire, envoy to NATO; Thomas Anderson, Barbados; Arthur H. Davis Jr., Paraguay; Lev E. Dobriansky, the Bahamas; David B. Funderburk, Romania; Jean Gerard, UNESCO; William A. Hewitt, Jamaica; David Jordan, Peru; Robert Keating, Madagascar; Alberto Piedra, Guatemala; Frank Ruddy, Equatorial Guinea; Richard L. Walker, South Korea; Curtin Windsor Jr., Costa Rica; Richard Williamson, International Organizations in Vienna; and Howard Eugene Douglas, ambassador at large.