When Ronald Reagan was a novice governor of California in 1967, the conventional gossip was that Nancy Reagan was running the state.

Evidence for this assertion was always on the thin side, but Gov. Reagan's good manners unfailingly reinforced the view that his wife was a power in the government. Unlike many executives, Reagan would interrupt a Cabinet meeting to take his wife's telephone calls. He also quoted her, further fueling reports that Nancy called the shots.

This talk is rarely heard these days, but Nancy Reagan is far more influential now than she ever was in Sacramento. During President Reagan's 23-day vacation in California, the First Lady has had full control of his schedule and effectively isolated the chief executive even from his own staff. She also has been politically active, as when she encouraged key Republicans in their attempt to talk Sen. Paul Laxalt (R-Nev.) into seeking a third term.

White House chief of staff Donald T. Regan and national security affairs adviser Robert C. McFarlane have been limited by Nancy Reagan largely to written communications and telephone conversations with the president. She has directed that all press interview requests be postponed, partly because she does not want the president disturbed by aides coming to the ranch to brief him. She has insisted that nothing be added to her husband's schedule without her approval, and she called for cancellation of a side trip to London when Reagan goes to Geneva in November for the summit meeting with Soviet leader Mikhail Gorbachev. The side trip was scrapped.

The First Lady's motive has been the laudable one of protecting the president while he recuperates from the operation that removed a cancerous tumor from his colon. But, in performing this protective role, she has become logistical director of the White House staff with wide jurisdiction.

It was Nancy Reagan who directed that aides withhold information that the small pimple removed from the president's nose was cancerous and who, according to some officials, did not even tell her husband until the day after she learned this information. And it was Nancy Reagan who fired her press secretary when this misplaced public relations effort went awry.

The First Lady has won grudging admiration even from White House detractors for the determination with which she has protected her husband. It may turn out that in doing so she has given the 74-year-old president a chance to recuperate fully from an operation that would have sidelined many younger people longer than it has Reagan.

Increasingly, however, there are those in the White House who worry that the protective blanket thrown around Reagan during his time at the ranch has distanced him from major problems of his presidency at a critical time. Some question whether he is being adequately prepared for his autumn dealings with the Soviets, culminating in the summit meeting. Others say the distancing shows up especially on the issue of South African sanctions, which Reagan intends to veto next month despite warnings that Congress could override his veto.

The president has usually been politically isolated during his stays at Rancho del Cielo, his ranch in the Santa Ynez Mountains. During the 1984 reelection campaign, Reagan became so hardened in his opposition to taxes during his ranch stay that political adviser Stuart K. Spencer was dispatched there to modify his stand and work out the "taxes only as a last resort" line that became the president's standard response on this issue.

Reagan's isolation now could have potentially serious consequences if he returns to Washington next month without understanding the growing restiveness among Republican members of Congress on a range of issues, including the budget deficit, tax reform and South Africa. Reagan also needs to deal with the conflicts within his administration on arms control well before he sits down with Gorbachev.

The president may demonstrate that he is up to speed on all these issues, but there's no way of telling that in Santa Barbara. Only Nancy Reagan knows for sure.

PREDICTION OF THE WEEK: Last week in this space, I said my "best guess" was that Sen. Laxalt would run again. Actually, it was my worst guess of the summer. But it isn't often that a popular senator turns down both the first family and his own, as Laxalt did, to do what is in his heart. More power to him.