SHORTLY BEFORE he became his party's leader in the House, Rep. Robert Michel observed about some of his more junior colleagues: "We've got a lot of kids who are used to lobbing grenades." Now, he would tell them, it is time for all congressional Republicans to compile their party's own record rather than to criticize the other fellows.'

For the other fellows, the Democrats, who were stripped by the November elections of their majority in the Senate and left with a greatly reduced complement in the House, there is a certain freedom that may compensate for the shock and "withdrawal symptoms" from lost power and surrendered chairmanships. For at least the next two years, the prime responsibility for finding the necessary votes for, say, raising the statutory debt ceiling or for passing the next administration's foreign aid bill will reside mainly with the Republicans on the Hill and in the White House. Democrats, unless their consciences so require, will not have to make themselves vulnerable to the cheap-shot demagoguery of the opposition for increasing the national debt by another five dozen billion dollars. It will be the GOP's turn.

Democrats will be able to point out the gulfs that will develop between Republican rhetoric and reality. Some of them have been practicing for these new responsibilities already. Their basic strategy appears to be one of holding the president-elect and his party accountable for the promises they made: to balance the budget, to cut inflation, to increase defense spending and to cut taxes. How will they do all these wonderful things simultaneously? the Democrats will ask. And they will recall how Rep. John Anderson answered the question during the Iowa Republican debate nearly a year ago: "With mirrors," he said.

Still, the Democrats cannot safely evade all responsibility. They control the House, after all. In every Congress, the conference committees that resolve the differences in similar legislation passed by the two Houses are crucial to the avoiding of legislative deadlock. Next year, with different parties controlling the two houses for the first time in 49 years, those conferences will demand very special legislative skill and leadership.

Democrats, in general, must forge responses to the new realities of, for example, decontrolled energy and near-permanent double-digit inflation. Attentive and conscientious constituent casework will no longer suffice. They alone do not carry the responsibility for authoring alternatives. But Hill Democrats are the most visible and the most politically exposed of all their party. Plenty of offers of help and counsel will be available to them. Democratic governors are obviously important and are potentially the sources of some wisdom and insight. Mayors and former and future officeholders and non-officeholders will be involved and their ideas sought.

The Democratic Party, which for most of this century has been the more activist of the two parties, seems to have lost some confidence in its own programs, and, to some degree, in itself. That is not like Democrats at all. The Democrats on the Hill are in the best position of all the party's members to do something about that. If they don't, the odds are long that the party's role as a constructive opposition force will be basically unmet for the next two years.