Faced with major organizational and financial problems. Sen. Howard Baker (R-Tenn) has drastically scaled back his campaign for the Republican presidential nomination.

Baker, according to advisers, has decided to concentrate his time and limited resources on early primaries and precinct caucuses in Iowa, New Hampshire, Illinois, and, to a lesser extent, Arkansas. He had previously intended to actively contest all early primaries.

This represents a major shift in strategy and means the Senate minority leader has decided -- at least temporarily -- to concede most of his native South to GOP rivals John Connally had Ronald Reagan during the early rounds of the race.

In addition, the Baker campaign staff is undergoing a major shakeup following the replacement of his campaign manager, Donald Sunquist, two weeks ago.

Yesterday Bernie Windom, political director of the campaign, resigned. This followed the replacement of William Savard, head of Baker's Iowa operation, and Chick Cudlip, his chief advance man and scheduler. Other high-ranking staff members are being reassigned from Washington to field operations in New Hampshire and Iowa. More changes are expected.

Baker, who has spent most of his time in the Senate while his rivals have campaigned, has also reluctantly agreed to go on the campaign trail on a full-time basis and yesterday informed his Senate colleagues of that move by letter.

The moves all coincide with a general realization in the Baker camp that the Tennessee Republican's presidential campaign is in trouble.

We're going to take our lumps in this campaign. We're going to be very hard put to win in Iowa," said campaign manager Wyatt Stewart in an interview. "We're going to have difficulty in New Hampshire."

Stewart, formerly the fund-raising director of the Republican Congressional Committee, was recruited for his job after Baker suffered an embarrassing defeat by George Bush, has chief rival in the moderate wing of the Republican party, in a straw poll at a GOP find raiser last month in Portland, Maine.

Baker was persuaded to devote full time to his presidential effort by his campaign chairman, Sen. Richard Lugar (R-Ind.), and his media adviser, Douglas Bailey, who has emerged as the chief strategist in the campaign.

Baker initially resisted pressures to campaign full time, Lugar said. "Howard wasn't sure he should break away. It's very tough for him to break away from his place.

"In the best of all worlds, someone ought to be able to serve in a public office and campaign for president. But that doesn't seem to be the case anymore."