Having seen "ships going both ways" in two visits to the Panama Canal earlier this year, Sen. William L. Scott (R-Va.) is off to Asia in search of the Khyber Pass.

Accompanied only by his wife, Inez Scott left last Friday on a 24-day tour of India, Pakistan and Afghanistan, after sealing the lips of his staff about the purpose of the junket.

No one seems to want to take credit for arranging the trip. Scott instructed his secretary to give copies of two letters by Senate president pro-tem James O. Eastland tht authorized the trip to anyone who inquired about it.

The Eastland letters, addressed to Secretary of State Cyrus R. Vance and Secretary of Defense Harold Brown, say that Scott proposed the trip "in connection with his responsibilities as a member of the Senate committees on armed services and judiciary . . . for the purpose of studying military and political affairs and reporting to the Senate . . . For reasons of protocal and attendance at official functions. Mrs. Scott will accompany the senator on this trip at no additional cost to the government."

Eugene Krized, director of congressional services at State, said Scott met with ambassadors of the three nations before leaving and was briefed by State Department official.

During one of those meeting in his Senate office, Scott reportedly interrupted the discussion to ask, "Now where is this Khyber Pass?"

Scott was told that the famous mountain break is on the Pakistan-Afghanistan border, a scenic spot through which legions of Persians, Greeks, Tatars, Mongols and British have passed over the centuries.

According to a cable received at State since Scott's arrival in India, arrangements have been made for the senator and his wife to be driven in an embassy car to the Khyber Pass, with time set aside for sightseeing on the border. The Scotts are scheduled to arrive at the pass at noon on Nov. 13.

Scott, said by some Senate aides to be one of the "most traveled" senators, told one State Department official he selected India, Pakistan and Afghanistan for his third foreign trip of 1977 because "I've never been there before."

Counting trips earlier this year to Panama (twice), Colombia, Argentina, Peru and Brazil, the three Asian countries will raise to be at least 37 the number of countries Scott has visited at taxpayers' expense during his five years in the Senate.

His proclivity for foreign travel was interjected in the Virginia gubernatorial race during a debate in Richmond recently when Democratic nominee Henry Howell admitted that he didn't know much about the Panama Canal, but added that he "hadn't been there twice either."

Scott, who has announced he will retire from the Senate in early 1979 after serving one term, has not been active in this year's Virginia election campaign.

The trip also caused Scott to miss a key vote Tuesday in the Judiciary Committee, which approved revision of the nation's criminal laws and sent the bill to the full Senate. Because he plans to return to the private practice of law when he leaves office, Scott said at the start of this year that he planned to focus his legislative duties on the Judiciary Committee.

A staff employee at the committee yesterday said there was no record that Scott plans to charge the trip, for which he is entitled to up to $75 a day in expenses, to Judiciary.

"No one here knows about it," she said. "I sure hope he isn't there for us, but he could come back and put in voucher."

At the Armed Services Committee, a spokesman said, "We don't discuss senators' trips."

At the Pentagon on Army spokesman said that her branch of military "provided no assistance . . . no escorts . . . we're not paying for it."

Army records showed that Scott and his wife drove to the Dover (Del.) Air Force base, where they left on an Air Force C-141 for India, via Ramstein, West Germany, and Teheran, Iran. They are scheduled to return Nov. 20.

An Air Force spokesman said, "We have nothing to do with it. He's on an Army trip."

Asked about the purpose of the trip, Sen. Eastland said yesterday that Scott was "investigating" for "both committees" on which he serves.

Investigating what? Eastland was asked. "Hell, I don't know. He told me, but I forgot."

Did Eastland see the latest Scott trip as an abuse of senatorial traveling privileges?

"No abuse," said Eastland, chomping on a cigar. "No more than any other trip."