The Reagan budget strategy now is emerging. From within the high reaches of the administration comes this admission, expressed privately to the Monitor:
* President Reagan right now is in a ''hard bargaining'' period. He appears to be adamant about giving no concessions on his budget. But realistically, an administration source says, he expects to agree to a compromise, perhaps as early as May.
The President, much as he once did as a union negotiator and as governor of California, is mustering his strength so that he can strike the best possible budget bargain when the time comes.
That's what his many meetings with leaders of Congress are all about. And that's what his current speaking tour aims to do.
Mr. Reagan, as administration sources now admit, is seeking to rally as much support behind him as he can before he sits down with the GOP's congressional leaders, Sen. Howard H. Baker Jr. and Rep. Robert H. Michel, and others to negotiate.
* The President does not want, and probably won't accept, any change that would eliminate or delay the July 1 tax cut now in place. A White House official says, however, that House minority leader Michel's proposal to advance the 10 percent tax cut to April 1 would be accepted by the President with ''enthusiasm.''
* In the end, Reagan likely will accept (a) some ''revenue enhancements'' (i.e. new taxes, such as excise taxes), (b) an end to the tax-leasing provision, which allows businesses to ''lease'' their tax breaks to each other, and (c) elimination of tax indexing, which was supposed to begin in 1985 and prevent taxpayers from suffering income tax ''bracket creep.''
* The President still is convinced that the bulk of the American public believes in his program and that it wants him to stay on course. That is why, administration sources say, he will refuse to go along with any alternative that cuts deeply into his defense budget or his spending and tax cuts.
* Reagan already feels he has won a commitment from Republican congressional leaders to try to come up with an alternative budget that will be, as one administration source says, ''very close to the President's proposal.''
Thus the President already is sensing some signs that his budget is winning out.
''We think in the end,'' one Reagan associate says, ''the alternative program will be one that Reagan can accept and also one that will draw behind it the GOP-Democratic conservative coalition that put over the President's economic initiatives last year.''
This source added: ''But if Congress comes up with a program that cuts too deeply into the President's approach and objectives, don't look for him to accept it. He'll veto (it) and go to the American people with the charge that Congress, or certain elements in Congress, was preventing him from putting in place his formula for helping the economy.''
* The President is basing his strategy on a new in-house poll, which tells him that the majority of Americans still approve of his economic program and the way he is handling his job. Reagan discounts a new Harris poll that says most Americans think his approach isn't working.
GOP national chairman Richard Richards, who has recently returned from traveling around the US, says that the people he talked to are supportive of Reagan and his program. Speaking at a breakfast meeting with reporters March 4, he said Americans are patient with Reagan and feel that he is on the right track and should stick to his course.
''I think that the President will get more than a lot of people think he will ,'' Mr. Richards says in describing the budget compromise. ''He is very persuasive - and there won't be much he will have to compromise.''
''But,'' he adds, ''he will compromise. He is not an all-or-nothing person.''