The administration is considering a second tier of tax proposals, including cuts in taxes on unearned income, Treasury Secretary Donald T. Regan confirmed yesterday. He told an audience at the National Press Club that if those at Treasury "had their durthers" they would choose to have two tax bills.

The first would be a "clean and simple" bill proposing ony accelerated depreciation allowances for business and a 30 percent cut in personal tax rates over three years. Then a second bill, which Regan said "would follow closely," could include a variety of measures such as a cut in the maximum tax rate on unearned income from 70 percent to 50 percent, taxing interest income at the lowest marginal rate rather than adding it onto earned income and "amerlioration" of so-called double taxation of dividends.

But the administration has not decided whether to go for that strategy or to include some of the additional tax proposals in the first bill. Office of Management and Budget Director David Stockman said yesterday that he doesn't "foresee the likelihood that there will be two tax bills passed by Congress this year" although he agreed that the administration may propose other "non-economic" tax measures later this year.

There almost certainly would be difficulty in persuading Congress to wait for a second tax bill before considering particular amendments favored on the Hill. Senate Finance Committee Chairman Robert Dole (R-Kan.) remarked after the National Press Club lunch that "if you were a hitchhiker, you wouldn't wait for the second ride."

Dole added that there would have to be a lot of discussion of the idea of a second bill. There is likely to be considerable pressure in Congress for reducing the "marriage Penalty," whereby married couples with two incomes are taxed more heavily than if there were single, as well as for a myriad of other tax measures.

The proposal for two tax bills is an apparent attempt by the administration to prevent negotiation and debate on all these measures from slowing the passage of the main tax proposals. Regan called these the "heart" of the administration's program.

He said that he would like the business tax cut to be made retroactive to Jan. 1 but that the timing of this and of the personal tax cuts have not been decided. He said that the tax and spending measures have to go together, like railroad tracks, and one without the other would be no good.

Regan seemed to suggest that the believes the size of the budget deficit is less important to inflation than whether it is "monetized," that is, covered by printing more money. This would be something of a switch from the administration's previous line.

The Treasury secretary also said that, although productivity growth would help to reduce inflation, money control has to do most of the job.

Stockman told a meeting of the American Business Conference yesterday that the administration will propose budget cuts of about $50 billion for fiscal 1982 which he said he does not think will be found "pro-Big Business."