Rosy Scenario has returned to the White House budget office. There had been a falling-out with the previous budget director, David Stockman. But he has gone into another line of work and been replaced by James C. Miller III. How can you tell that Rosy is back? By listening to Mr. Miller's advice this week to Congress. To avoid raising taxes or cutting defense spending, he suggested "correcting" -- his word -- the economic forecast upward and the spending estimates downward.

But the administration's economic forecast strains the limits of plausibility. As for the spending estimates, the Congressional Budget Office has warned that the administration underestimated some of them by substantial amounts -- in the case of defense, by nearly $15 billion. Mr. Miller thinks that the events of the past two months, such as the drop in oil prices, will automatically reduce the deficit. But hardly anyone else thinks so. The publication of Mr. Stockman's book makes this week a remarkably inopportune time for anyone from the White House to hint at further manipulation of budget figures. Rosy S. is a known offender, as most of Congress sees it, and is a bad influence on impressionable young men.

No doubt Mr. Miller's latest budget advice to Congress was a trivial incident. But it accurately reflects the irresponsible attitude that the White House has brought to this year's budget. Its own proposal, sent to Congress in February, was flawed both by bad judgment and bad figures. Since then, departing from the pattern of previous years, the president and his staff have flatly refused to negotiate any improvements.

The House Democrats, with more prudence than courage, have taken themselves carefully to the sidelines to wait until the Senate acts first. In the Senate, the chairman of the Budget Committee, Pete Domenici, with support from both Republicans and Democrats, has produced a budget that is greatly superior to Mr. Reagan's. It would slightly increase taxes, maintain the present level of defense spending, impose some nondefense cuts and arrive at a significantly lower deficit. It meets the deficit requirements of the Gramm-Rudman-Hollings Act, as the Reagan budget would not. The administration's position on G-R-H has been to support it in press conferences but to attack it in court -- as it was doing yesterday in arguments before the Supreme Court.

The budget has now come to the Senate floor a month later than its sponsors intended. The delay is the result of various senators' futile attempts to work out an agreement with the White House. But the budget now before the Senate is the Budget Committee's alternative, far fairer and more realistic than Mr. Reagan's. The committee's alternative, as it stands, is the budget for the Senate to pass.