Jesse A. Helms, the Senate's self-appointed conservative watchdog, yesterday said he put "holds" on a number of top State Department appointments because he had doubts the nominees share President Reagan's views on foreign and economic policy.

In an unusual letter outlining reasons for his actions the last several months, Helms (R-N.C.) said he felt it necessary to "alert" Secretary of State Alexander M. Haig Jr. and the Reagan White House of concerns conservatives share about the nominees.

"My only desire is to do whatever I can to try to assure that the policy-makers nominated in the name of the president actually reflect, to the fullest extent possible, the president's views," Helms wrote.

As a result of his tactics, several key officials charged with formulating foreign policy remain in a bureaucratic twilight zone almost 100 days after Reagan's inauguration.

These include assistant secretaries of state for three of the State Department's most important regional bureaus -- Latin America, Africa and East Asia.

Helms outlined the rationale for his actions in a 10-page, single-spaced letter to Senate Foreign Relations Chairman Charles H. Percy (R-Ill.). lIt was his most complete and formal explanation to date on questions he has raised over Reagan appointees, eight of whom he discussed point-by-point. Helms is the third-ranking Republican on the committee.

In the "Dear Chuck" letter, the North Carolina senator expressed "a little surprise" with press accounts criticizing him for "holding up" nominations, and he denied them. He said administration delays in forwarding nominees' names to the Senate have been the real cause for the confirmations taking so long.

Senators, he noted, are mandated by the Constitution "to offer such advice as each senator deems proper and later to give or withhold consent."

Helms raised questions about eight State Department nominees, but said his concerns about four have been eased. One of the four, M. Peter McPherson, was confirmed as administrator of the Agency for International Development after Helms questioned his views on abortion. The others have been working at their jobs without confirmation.

Helms directed his harshest criticism against Chester Crocker, the assistant secretary of state-designate for African affairs, who recently went on a 10-country trip to Africa.

"Mr. Crocker's performance in Africa, by accounts that I have received, bordered on being dismal," the senator wrote. "He was an embarrassment to the U.S. in both Mozambique and South Africa. Heads of state refused to see him. Instead of building new friendships for the U.S., he appears to have succeeded in antagonizing the left while alienating old allies.

"The question is: Does Mr. Crocker reflect the Reagan viewpoint on Africa as laid out by the president during the campaign? Is it not obvious that the president and our nation would be better served by another individual?"

Helms said he had placed a hold on nomination of John Holdridge, a career diplomat, as assistant secretary of state for East Asia because he "has encouraged a tilt toward the People's Republic of China which in no way is in tune with the tone, spirit or detail of President Reagan's campaign commitments" or the Republican platform.

Helms expressed similar doubts about Myer Rashish as undersecretary of state for economic affairs. "I have great concern," he wrote, "that Mr. Rashish does not support the president's economic and foreign policies." Helms also said he was worried that Rashish "may have mixed loyalities" because of his previous lobbying efforts for private firms in West Germany and France.

But the North Carolina Republican was gentler with a number of other nominees he had previously questioned. He offered only mild criticism, for example, of Thomas O. Enders, who was nominated last week as assistant secretary of state for inter-American affairs, a job John Carbaugh, one of Helms' top aides, had once sought.

He called Enders, a former ambassador to Canada and the European Common Market, a "highly qualified and dedicated civil servant." However, Helms noted Enders lacks experience in Latin American affairs and speaks neither Spanish nor Portuguese.He suggested Haig should have placed the former ambassador "in a post where his acknowledged qualifications could be more beneficially used."

The other nominees discussed in the letter were Lawrence W. Eagleburger, assistant secretary of state-designate for Europe whom Helms said was more "conservative" than he originally thought; Robert Hormats, a former Carter administration official and assistant secretary-designate for economic and business affairs, and Eugene V. Rostow, who has been designated to head the Arms Control and Disarmament Agency