THE MAN FROM MARS was back the other day. He had a couple of questions about the tax bill that the House Ways and Means Committee has just reported. He said he continues to find our political system peculier but interesting, and so whenever he's near this planet he stops by to bring himself up to date. On his last visit we explained how the country got itself into its present state - how two freely spending Democratic administrations under Richard Nixon and Gerald Ford ran up huge budget deficits, paying out unprecedented public benefits, until finally in 1976 the voters rebelled and elected a Republican administration under President Carter, who was committed to a balance budget, businesslike management and a firm limit on federal spending.

"Now, explain to me what's going on in the Ways and Means Committee," said the Martian. We're not sure we understand it ourselves, we warned him. "I thought you told me that there were 25 Democrats on that committee," he persisted, "and only 12 Republicans." That had certainly been our impression, we said.

"Then how does it happen that the committee produces a bill that is being applauded by bankers and business lobbyists as the strongest and finest Republican tax bill in 30 years?" the man from Mars asked. We suggested that it's beginning to look as though there had been a coup in the committee.

Consulting his notes, the Martian reminded us that under Mr. Carter's proposal last January, the biggest reductions would have gone to people making from $5,000 to $15,000 a year. But the Ways and Means Committee's bill gives the cuts mostly to people between $20,000 and $50,000 a year. We explained that the war on poverty is now being extended to the upper-middle classes. Congress wants to be fair to everyone, and it is trying to combat destitution with equal vigor at all income levels.

"I see that the bill would also cut the capital-gains tax and lower the corporate-tax rate," said the Martian. "What is the committee's purpose?" The committee, we emphasized, is deeply concerned about poor performance of business investment, industrial productivity and corporate profits.

"But I thought I read that it was the Republicans who worry about business investment, productivity and profits," said the Martian. That sed to be true, we explained, in the old days when investment, productivity and profit were all doing well. Now that they are lying flat, the Democrats are seizing them as political issues. Nobody knows what to do about them, but the Democrats think that something has to be done.

The Martian considered the point. "But don't the Republicans get angry when the Democrats steal their issues?" We said that, as long as the Republicans continue to win the votes on tax policy, they are prepared to be generous about sharing issues.

"I believe that you are holding congressional elections in November," said the Martian, who is developing a good grasp of the situation here. "Will all of those Democrats feel comfortable running for reelection on a Republican tax bill?"

"Maybe not entirely comfortable," we answered. "But they'd rather do that than run on their own energy bill."