THOUGH Mount St. Helens was still relatively quiet, frustrated Washington State tourism officials (not to mention officials of the Pacific Northwest Regional Commission) were ready to erupt recently.

The governors of Washington, Oregon and Idaho, whose states suffered a drop in vacation travel as a result of the publicity fallout after the mountain blew her top in May, felt the need to advertise in 11 U.S. newspapers: "Ashfall effects exaggerated . . . Traffic routes open . . . Don't let rumor ruin a vacation . . . call now."

And under a bold headline "What If It Happens Again?" the ad stated that while scientists don't believe Mount St. Helens is likely to repeat "the magnitude of her May 18 display . . . they disagree on whether she may burp more ash . . . Before you head our way, call the toll-free number . . . (1-800-426-8668 for Washington State) for the up-to-the-minute condition report." (Last Tuesday the mountain "burped" three times, sending a new cloud of ash drifting.)

In a further effort to counter a negative and incorrect impression that (as one Washington tourism spokesman put it) "the state was buried under six inches of ash" a group of about 60 journalists, magazine writers and broadcasters were recently given a 3-day tour of Washington and Oregon so they could see that most of those areas were "never affected." The trip was sponsored by United Air Lines in cooperation with the states and major corporations.

Also trying to dispel a negative image which they feel is unfair and causing many airline passengers to void flying in the DC-10, the McDonnell Douglas Corporation has published a booklet titled, "The DC-10 -- A Special Report."

It is "part of a multimillion dollar communications campaign aimed at making more widely known the findings of extensive investigations that have vindicated the safety and performance of the DC-10," according to the corporation which built the airliner.

Charles "Pete" Conrad, the former astronaut, who is now a McDonnell Douglas executive and principal spokesman in the campaign, said that "data to support the statements made in the booklet are readily accessible at the Federal Aviation Administration and the National Transportation Safety Board, the two organizations that have vindicated the DC-10."

A free copy of the booklet can be obtained by writing to Ralph Underdahl, Douglas Aircraft Co., 3855 Lakewood Blvd., Long Beach, Calif. 90846.

A third kind of image problem faces the Soviet Union, and those involved in sending visitors to that country at this time -- even a non-political, nonprofit organization like the Citizen Exchange Corps.

The U.S. boycott of the Moscow Summer Olympics in protest against the Soviet army's invasion of Afghanistan, eventually supported by many other nations, has caused thousands of American travelers to change their plans about visiting Russia this year. President Carter did not advocate a boycott of all travel to that country but, as one tour operator admitted March, "a de facto ban" was already in effect then due to strong feelings among American tourists.

Now the spectacle of massive Soviet security efforts at the Olympics, which not only eliminate any chance of anti-government political demonstrations but also any significant opportunity for contact between foreigner and Soviets, have added to the bitterness.

With the Kremlin issuing warnings to its citizens about foreign provocateurs bringing timebombs or anti-Soviet literature, it becomes under-standable why the Citizen Exchange Corps is having some difficulty getting enough Americans to sign up for its package trip to Siberia and Mongolia via the Trans-Siberia Railroad. The tour is scheduled to leave Sept. 15 from New York, and a spokesman acknowleged that the fallout from Afghanistan is "definitely affecting our efforts" to book the tour.

The CEC, at 18 East 41st St., New York 10017, has been working for 17 years "to improve understanding by bringing American and Soviet citizens together on a person to person level." In March, then Secretary of State Cyrus Vance told the CEC that "It remains our policy to encourage such private activities . . . we have sought to avoid dismantling the framwork of exchanges and cooperative activity developed with such great effort over the years." Vance noted with satisfaction that CEC was not planning "any travel to Moscow during the Olympics.