For a member of Congress, there's a thin line between properly representing a constituent with a gripe against the government and improperly twisting arms.

Ethics monitors have been trying for generations to determine how and where that line should be drawn. They haven't succeeded yet.The subject is once again at issue in the ethics case against House Speaker Jim Wright, even though the House Ethics Committee decided not to press charges over his heavy-handed intervention with federal regulators on behalf of Texas savings and loan interests.

Rep. Newt Gingrich, R-Ga., Wright's original accuser, says he thinks the S&L accusations will be revived if charges against the speaker involving outside income and unreported gifts come to the House floor for action.

Gingrich said Wright's intercession led to delays in House action while the problem worsened, and that the delays, in turn, may have added $40 billion to the cost of settling the S&L crisis.

Both his points are hypothetical, but they illustrate the problem a member of Congress can face when he takes up the cause of a constituent who is having trouble with the federal government. There's no telling where it might lead.

Yet, for the member of Congress who wants to remain one, intervening for constituents with problems is essential work. It is part of the process of representing a district or a state. It also is one of the ways Congress oversees the executive branch.

From the missing Social Security check to the overzealous regulator, that kind of intercession can solve problems. Besides, this year's constituent with a problem solved becomes next year's voter, donor, perhaps campaign volunteer.

The trouble is that it is hard to determine who really is out of bounds - the constituent or the civil servant. A Senate panel tried to set guidelines as far back as 1951, and wound up offering advice instead of rules.

"A legislator should not immediately conclude that the constituent is always right and the administrator is always wrong," wrote Paul H. Douglas, the late Democratic senator from Illinois, who headed that ethics subcommittee. He said the senator or representative should investigate, try to determine the merits of each case and proceed accordingly.

That advice was cited by Richard J. Phelan, special counsel to the House ethics committee, in his report recommending that Wright be charged with improperly pressuring the Federal Home Loan Bank Board in behalf of Texas savings and loan operators.

A House ethics report in 1970 said members are in bounds when they seek information about cases before executive or independent agencies, arrange appointments, make judgments and ask for reconsideration of decisions they think are not supported by law.

The report also said the member of Congress' services should be provided to all constituents on an equal footing, without regard to politics or position; and that any suggestion of either favoritism or reprisal against the agency involved "is unwarranted abuse of the representative role."

The Douglas subcommittee said pressure against federal agencies through "hostile action in budgets or legislation is a kind of blackmail which is damaging to the public interest. . . ."

At the same time, the Senate panel said members of Congress should intercede for their constituents so long as they do it with proper restraint, "for civil servants frequently become perfunctory in their work and careless of the people whom they are presumed to serve.

"Legislators can, therefore, legitimately serve as an informal board of inspectors," the subcommittee said. "They can prevent administrators from flagging in their zeal and can detect and check abuses in the conduct of public business."

But the panel saw ethical quicksand in efforts by members of Congress to get favorable rulings for constituents in specific cases. It said legislators should insist on fairness but shouldn't try to force specific outcomes.

That sounds simple. It isn't. When a government agency is ruling on a case vital to an individual, a business or a group, the people involved are likely to see fairness in only one outcome.

In the end, the individual member of Congress has to decide what's fair and proper. When those decisions come due, no rule book can substitute for conscience and common sense.