The arduous process of developing policy options on acid rain is headed into extra innings, and the outcome is far from certain.

Environmentalists, cheered by indications that an Environmental Protection Agency task force is considering requiring significant reductions in sulfur dioxide emissions, figure it's just a question of how much the agency is willing to do and how soon.

Some industry representatives, eyeing the growing pile of congressional proposals, are laying their bets the same way. In recent weeks, the low-sulfur coal and natural gas industries have been spreading around a variety of let's-be-reasonable-about-this proposals that promote their products as a cost-effective alternative to expensive sulfur-scrubbing equipment.

But the EPA's late-August deadline for submitting options to the White House has slipped, first to late September, now to "sometime in October." No one is hazarding a guess as to when President Reagan will make a decision.

Asked this week if Reagan was convinced that steps needed to be taken to curb the sulfur dioxide emissions linked to acid rain, EPA Administrator William D. Ruckelshaus replied: "I don't think so."

Sometime next month, Ruckelshaus will hand Reagan four possible strategies. In a meeting with reporters this week, the EPA chief emphasized that the administration's current research-only stance has always been one of the options.

Among the other options reportedly being considered are a 31-state, 10-million-ton sulfur reduction that is favored by environmentalists; a 21-state, 8-million-ton reduction; and a "targeted" reduction, involving from four to 10 states and four million tons of sulfur.

The targeted reduction would be aimed at easing damage to lakes in the Northeast while serving as a demonstration project to determine the need for future reductions.

The drawback to any of the strategies is, of course, the question of who is going to pay and how. Proposals range from taxes on high-sulfur fuels to taxes on emissions to production-based taxes, such as a levy on the amount of power generated by a coal-fired power plant.

"There is no tax that is equitable to everyone," said Ruckelshaus, who has been spending a large chunk of his time in meetings with the potential winners and losers, as well as with administration officials.

Questioned about a session this week with White House political director Ed Rollins and long-time Reagan adviser Lyn Nofziger, Ruckelshaus replied drily: "We talked about the need to purify the lakes in New England." * * *

TOXICS UP IN THE AIR . . . The EPA has a tough row to hoe in attempting to control toxic air pollutants, the General Accounting Office has concluded in a report that attributes the agency's slow progress to policy shifts, scientific uncertainties and the fact that there are only 24 hours in a day.

But the GAO found little justification for the EPA's position that it can take "dire economic consequences" for industry into account in deciding what standards to set for airborne pollutants that can cause cancer and other ailments.

The point is critical to Ruckelshaus' recent decision to ask the citizens of Tacoma, Wash., whether they would accept a risk of cancer from airborne arsenic emissions if the alternative was to close a copper smelter that is a major local employer.

The EPA has managed to start the regulatory process on only seven toxic air pollutants; it has taken no action on 37 identified since 1977.