It is almost a year now since the roof, the stars and 49 states fell on Walter Mondale's head. The visible scars -- the deep rings around the eyes and the cracked voice -- have disappeared. The man who sits behind the desk in his Washington law firm looks a bit plumper and much more rested than the candidate who plowed doggedly ahead 52 weeks ago, heading for what he knew would be a thorough beating.

No one, however, recovers quickly from a losing presidential race. Mondale is honest enough to describe his law practice as "good therapy" for his shattered ambitions. And he expresses genuine relief when a visitor says he would rather talk about current politics and policy than rehash the last campaign.

As it happens, Mondale has some interesting thoughts to offer -- some old, some new. As in the campaign, he puts deficit reduction at the top of the domestic agenda, and he disagrees with the majority of Senate Democrats that the Gramm/Rudman "automatic cutback" mechanism is the right way to go after the deficits.

"I would have voted against it," he said, thus aligning himself with the 20-member minority of the Democratic minority. "That approach leaves the damage unspecified, but it gives the president the whip hand. . . . He can veto Congress' budget. He can veto any tax increase. Then when he makes his cuts, you can't get a two- thirds majority (in Congress) to override him. I'm afraid it would allow him to repeal wholesale the programs that he's attacked piecemeal."

Mondale's position puts him in agreement with his principal 1984 adversary, Sen. Gary Hart (D-Colo.), for whom he has warm words of personal and political praise these days. It puts him at odds with his fellow liberal, Sen. Edward M. Kennedy (D-Mass.), who supported both the Gramm/Rudman proposal and the earlier unsuccessful Republican effort to give President Reagan line-item veto authority.

Kennedy defended both votes as necessary to strengthen the authority of the presidency and to deal with deficits. But Mondale said, "I don't accept" that rationale. "The line-item veto involves a grievous diminution of Congress' constitutional power," he said. "And if we gave that power to this particular president, there is no way we could maintain the programs that we need to keep this a decent society.

"You just look at the rescissions (the requests for revocation of certain spending programs) that Reagan has sent up (to Congress) and you know what he'd do. In my judgment, those who support such measures as the line- item veto are endorsing an abdication of congressional responsibility."

The reason that Democrats find themselves still on the defensive on the budget deficit issue, Mondale says, is that "we haven't made the case successfully -- certainly I didn't during the campaign -- that a tax increase is necessary." Mondale has not wavered in that analysis, however.

"We have to face the need to pay our bills," he said. "We have to get the deficit down. It's the source of 80 percent of our trade problems, of our agriculture problems, of our industrial problems.

"I might even make a deal with the president to accept more regressivity in our tax system in order to get the deficit down," Mondale said. Ideally, he would like to see the tax- reform bill now being fashioned in the House used as a vehicle to close loopholes, broaden the tax base on corporations and individuals, and raise more revenues through the progressive income tax.

But if Reagan's veto threat prevented that, he said, he would support a value-added tax, a form of excise or sales tax used in many European countries: a tax on consumers. "As president, I never would have accepted a value-added tax," he said, "but if it's necessary to get us out of this radical impasse on the budget that Reagan's policies have created, I would do it."

Despite his strong rhetoric last year on the trade issue, Mondale is swinging back to the more liberal trade position he held as a Minnesota senator and a member of the Carter administration. He opposes the textile bill, which went whooping through the House and which faces a Reagan veto if it goes that far.

He endorses less drastic measures aimed at opening foreign markets to U.S. goods and curbing other countries' unfair trade practices. But he said, "If the president gets serious about trade policies and the deficit, a lot of the protectionist pressure will relax. If we adopt a defeatist-protectionist policy as a nation, we will be the loser."

On these and other topics, Mondale is not reticent. But he's not pressing either. He made one speech to a Democratic fund-raiser early this month and will talk to the Council of Foreign Relations in November. He expects to be helping some Democratic candidates in 1986, but "nothing that resembles a campaign schedule." He's done that, and he hasn't forgotten what happened.