President Reagan will make a nationally televised appeal for his $98.9 billion tax bill as part of what aides termed "an all-out effort" to win approval of the measure, which has provoked a revolt among previously loyal House conservatives.

Administration sources confirmed yesterday that Reagan wrote a draft of the speech last weekend and that he probably will deliver it during prime time Monday from the Oval Office.

They said the president has reached a definite decision to make the public appeal, but has reserved a final decision on its timing pending the report of a Senate-House conference committee on the tax increase bill.

While administration officials promised that Reagan would employ his celebrated abilities as "the great communicator" on behalf of his tax bill, they attempted to play down a report that presidential consultant Lyn Nofziger had threatened recalcitrant congressmen that the administration would withdraw support in the midterm elections if they vote against the tax bill.

"That's just talk," said Rep. John Rousselot (R-Calif.), a longtime Reagan supporter, a friend of Nofziger and an opponent of the Senate-passed tax bill. "There were seven Cabinet members at my reception last night."

The Cabinet members, including Treasury Secretary Donald T. Regan, received free tickets, but were drawing cards at the $250-per-person reception that raised an estimated $30,000 for Roussellot's reelection campaign.

There were published reports yesterday that Cabinet members were instructed, in Reagan's presence, not to campaign for any congressman who opposed the tax bill.

The reported "instruction" came from Nofziger, a former top Reagan political and communications aide, who has been brought back into the White House as a consultant to help pass the tax bill.

Yesterday, however, both GOP congressmen and administration officials said that Nofziger, known for his hard-hitting campaign tactics, had "reformulated" his statement to say that the tax bill would be "one consideration" when political suppport was decided.

Some officials pointed out that, as a practical matter, the White House was in no position to insist on blind loyalty on the tax bill.

The coalition that is likely to support it will not be like the alliance of nearly all House Republicans plus conservative "boll weevil" Democrats that has been the key to the administration's past success.

The probable coalition on the tax bill ranges from moderately conservative Republicans to liberal Democrats with a number of conservative defections likely in both parties.

The White House began its campaign for the tax bill with support from only one of the 21 California Republicans, who have been a special target of administration lobbying.

Asked how the White House was doing in its campaign to convert Californians, who until now have been almost uniformly loyal to Reagan, Rousselot replied, "They're making progress--they're up to three."

Nevertheless, well-placed administration officials yesterday predicted that Reagan would prevail--as he has in the past--through a combination of intense lobbying and his own televised powers of persuasion.

These officials said Reagan himself advocated the nationally televised speech, believing it is the most effective means of indirectly persuading Congress.

But he also will hold a series of meetings with groups of congressmen and, if necessary, with individual holdouts.

White House chief of staff James A. Baker III also is playing a key role in the tax fight. He addressed a closed session of conservative congressmen Tuesday night, telling them that as difficult as it would be to campaign after the the tax bill passes, it would be more difficult to campaign with the high interest rates that would result from its defeat.

There were mixed reviews of Baker's speech. One conservative said he had made "an effective presentation" while another called it "a Rotary Club address that told us everything we already knew."