Sen. Adlai Stevenson (D-Ill.) proposed yesterday that the administration's bill to impose a tax on the "windfall profits" from oil price decontrol be expanded to include a 50-cents-a-gallon tax on gasoline sold to noncommercial consumers.

As a senator who is not seeking reelection, Stevenson could lob such a legislative grenaded onto the Senate floor with political impunity.

But if it shook up the Senate, it was not apparent from the initial reaction. Those few senators who were sitting around marking time when Stevenson proposed his amendment simply maintained that posture.

In effect, the Senate bided its time with speech making and procedural squabbing yesterday in anticipation of votes on two critical issues today.

One vote will come on a proposal to raise the anticipated yield of the tax by 1990 from roughly $155 billion to $185 billion. The other will occur on a move by Senate Majority Leader Robert C. Byrd (D-W.Va.) to impose cloture to restrain debate and block extraneous amendments. Stevenson's amendment could fall in the extraneous, or nongermane, category.

The votes on both issues are expected to be close. They could also be decisive in telling how far the Senate will go in strengthening its version of the tax bill -- and whether it can finish by its scheduled Christmas recess on Dec. 21 or 22.

The administration pushed hard for the increase, which would come from imposing a 20 percent "minimum tax" on the decontrol windfall from certain categories of oil -- including newly discovered oil -- that otherwise would be exempt from the tax. Treasury Secretary G. William Miller lobbied for the proposal on Capitol Hill, and White House press secretary Jody Powell said President Carter spent part of the day seeking support for it.

In a brief flurry of activity last night, the Senate rejected, 65 to 8, an amendment by Dennis DeConcini (D- Ariz.) that would have given law enforcement officers access to a person's tax returns without a court order.

A 50-cent gasoline tax, which the Carter administration is considering along with gas rationing in an effort to curb oil consumption, has also run into problems in the House.

Speaker Thomas P. (Tip) O'Neill (D-Mass.) told administration officials Monday that the House would probably resist a gas tax increase, and yesterday House Majority Leader Jim Wright (D-Tex.) wrote a letter to President Carter expressing his opposition to a 50-cent increase.

Wright said such a tax would be unfair to people who must use cars in their work, describing it as "rationing by price" for low-to-moderate-income Americans. He said it is a "harsh and punitive approach since it forces conservation first and foremost on the poor."

Wright also opposed the idea of making Social Security payments taxable and said both the Social Security and gas tax approaches would have a "difficult time" in Congress.

In outlining his gas tax proposal, Stevenson contended it would raise nearly $40 billion a year that could be used for a variety of purposes, including assistance to the poor. By exempting commercial users of gasoline, it would have only marginal impact on inflation, he argued.