Republican Party officeholders begin their fifth annual Tidewater Conference in Easton, Md., today still convinced that President Reagan is too popular personally to challenge openly, uneasy that they are hostage to his programs, which many supported more out of loyalty than conviction, and irritated with Sen. Bob Packwood (R-Ore.) for publicizing their internal conflicts.

GOP leaders say the conference, intended to produce policy positions that most of the party can endorse, is likely to be rockier than its predecessors because of uneasiness about the economy's effect on their election prospects and Packwood's contention in a recent interview that Reagan is weakening the party by ignoring women, blacks and other minorities.

In a sense, the different mood of the conference reflects the Republicans' new political prosperity. It worked well when first created in 1978 as a forum for the minority party to articulate its policies.

The GOP's recent successes, however, have been accompanied by the increasingly severe stresses Reagan's policies have put on many Republicans, particularly in the Northeast and Midwest. Some Republicans now see the conference as more an opportunity for young senators and House members to speak out publicly than as a unified policy forum.

Some conservative senators have called for Packwood to resign as chairman of the Senate Republican campaign committee but there appears to be little support for it. There was as much irritation with Packwood, a founder and leader of the Tidewater Conference in 1978, for the four controversial resolutions he put on the agenda.

About 100 Republicans were scheduled to attend the two-day conference, including Senate Majority Leader Howard H. Baker Jr. (R-Tenn.), four Cabinet officers, eight senators, 30 House members, Republican National Chairman Richard Richards and governors and state party leaders.

The resolutions are: That the United States "maintain all options, including the use of armed forces, in order to protect our interests in Latin America"; that the Republican Party opposes the "legislative curtailment of the jurisdiction of the Supreme Court of the United States or the inferior federal courts for the purpose of effecting changes in constitutional law"; that Congress take the steps necessary to achieve the goal of a balanced budget by 1985, and "that the federal government return to the states the responsibility for the maintenance of the health, education and welfare of its citizens, along with the funding resources necessary to support such programs and responsibilities."

"El Salvador and the jurisdiction of the courts are not Republican issues," said Sen. David F. Durenberger (R-Minn.). "You never know why Packwood chooses the subjects he does. He sent out letters to everyone and this is what boiled up."

In addition to their conviction that their own electoral success depends on the success of Reagan and his programs, many Republicans don't want to undercut the president.

"There's a concern for the presidency itself, that the country gets caught if there's a savage crossfire between the president and Congress and the president gets pulled down," said Sen. William S. Cohen (R-Maine). "We want to do everything to help him."

Sen. Slade Gorton (R-Wash.) agreed. "Everyone is still very supportive of the president and his goals," he said.

Only Sen. Larry Pressler (R-S.D.) is willing to criticize the president openly. "The president is losing touch," he said, echoing Packwood's words. "The Republican Party should be the party of Main Street, not Wall Street. I think there will be a political revolution in my state unless interest rates come down."