Campaign strategies shift

Politicians call it ''Big Mo.'' It's the momentum a candidate feels when good things start happening - one after another. This week, it has finally been Walter Mondale's turn to enjoy a little bit of ''Big Mo.'' You can see it in the enthusiastic Mondale crowds. You can see it in the smiles of the Mondale staff. And you can see it in the polls.

Over at Reagan-Bush headquarters, they're suddenly being forced to deal with adversity for the first time this fall. All over this city, damage-control switches are being thrown by Republicans in the wake of the the Reagan-Mondale debate, which even a Reagan friend like US Sen. Paul Laxalt (R) of Nevada now says the President ''lost.''

Senator Laxalt vows that in the next debate on Oct. 21, America will see ''a brand-new Ronald Reagan.'' The mistake last time, Mr. Laxalt says, was that the White House staff smothered the President with facts and figures, then ''brutalized'' him by making him go through six full-fledged dress rehearsals. That was done during the period when the President was in the midst of crucial meetings with Soviet Foreign Minister Andrei A. Gromyko.

Next time there will be far less preparation, and the staff will just ''let Ronald Reagan be Ronald Reagan,'' says Laxalt, who is chairman of the President's campaign.

Meanwhile, both camps now await fresh signals from the polls. Those numbers could shape the remaining 25 days of this race and tell whether Mr. Mondale has any chance of pulling one of the most astounding upsets in history.

Private polls taken by both Peter Hart, the Mondale pollster, and Richard Wirthlin, the Reagan pollster, are getting similar results at the moment. Two important sets of numbers are considered crucial.

The first set of numbers involves Mr. Reagan's lead. Prior to the debate, both sides were estimating the President was ahead by about 17 or 18 points. As of Thursday, that lead had shrunk to 13 or 14 points.

Robert Beckel, Mondale's campaign manager, says that to make a race of it, Reagan's lead should drop below 10 percent by the end of next week. If that happens, and if Mondale could again score in the Oct. 21 debate with Reagan on foreign policy, victory could be within sight, Mr. Beckel says.

Charles Black, a Reagan strategist, says Republican polls agree that Mondale gained from the first debate. But Mr. Black sees Reagan's margin holding at no less than 12 percent within the next few days. If Reagan can sustain at least that 12-point margin through next week, any prospect of a Mondale victory could be lost, Black says.

Like a number of independent experts, Black insists that Mondale's gains are coming too late. At this rate, he says, it would take Mondale ''seven or eight debates ... to catch up with us.''

There is, however, a second set of numbers that has made the Mondale camp jubilant. As reported by the ABC/Washington Post poll, Mondale's favorable-unfavorble scores with voters have moved from a negative 41 to 49 to a positive 54 to 43. That's a rise of 19 points in one week - and experts say it could presage further Mondale gains against Reagan.

The news isn't all bad for Reagan, however. That same ABC/Post poll found that, after Louisville, Reagan's favorable-unfavorable rating stayed as strong as ever, at 61 to 36. It appears that voters didn't like Reagan any less after the debate, they just liked Mondale somewhat more. Mondale must find ways to whittle away at Reagan's favorable rating if voters are to have a reason to oust the President.

Each camp is now plotting its strategy for the final weeks. Here's the outlook from both sides: Mondale

Meeting with reporters here over breakfast, campaign manager Beckel went back to what has become one of his tried-and-true themes: volatility. During the primaries, he says, pollsters saw switches of 30 to 40 points among voters in as little as five days. Mondale's latest 19-point gain in his favorable rating was another indicator of volatility.

Mondale has now captured America's attention, says Beckel. For the first time , he has an opportunity to get his message across. Beckel sees Mondale hitting several points very hard in coming days:

Lebanon. Despite intelligence warnings, the US Embassy was vulnerable. Beckel calls that a case of ''administration-wide incompetence.''

Soviets. Beckel observes that Reagan is proud of standing up to the Soviets. But he asks: ''Have the Russians moved out of any place they were before he got in? No. Have they got any farther since he got in? Yes.''

Casualties. American troops have been killed in Lebanon, even though the US was not at war.

Arms control. No treaty has been signed under Reagan.

Human rights. Weak support from Reagan.

Central America. Less stable today.

Despite press and TV attention to the so-called age issue in the past few days, Beckel says: ''I don't think you're going to find us getting into that.'' Reagan

Republican allies of the President have swung into action this week in an effort to slow Mondale's gains. Thursday on Capitol Hill, several GOP senators called raised a number of points about the Mondale record. The senators asked:

- Why hasn't Mondale paid back, as promised, several hundred thousand dollars that was used in his behalf by political-action committees during the New York State primary?

- Isn't Mondale partly responsible for the current farm crisis, which has its roots in high inflation and interest rates from the Carter-Mondale years?

- Why is Mondale featuring F-14 aircraft and nuclear carriers in his TV ads when he voted against both of them as a senator?

- Why is Mondale trying to scare America's 36 million social-security recipients when it was Reagan who worked out the compromise that made the system solvent?

- Why has Mondale taken three different positions on tax indexing?