Don't look now, but George Bush is thinking again about momentum.

But in a most un-Texan like fashion, it's Little Mo, not the more celebrated Big Mo, that's on his mind.

This is Bush's fourth "home" state of the 1980 campaign, and the one where he has lived for much of the last 30 years. Bush won his other home states -- Maine, Massachusetts and Connecticut, but expects to see the string broken here by Ronald Reagan.

After his upset victory in Pennsylvania last week, however, his campaign here is filled with the metaphors of motion as he stumps through the urban area of Texas, the only places where his staff feels he can beat Reagan.

There is more, to sure -- and it includes his sharpest rhetoric yet against Reagan and blatant appeals for support from all Texans, Democrats, independents, blacks and Hispanics, all of whom are eligible to vote in Saturday's Republican primary.

So blatant is his approach, in fact, that on Monday night in Houston he paraded his Mexican daughter-in-law and her husband, son Jeb, before a partly Hispanic crowd where he got Jeb to "say something" in Spanish. The mostly uninterested audience, preferring bingo to Bush, booed briefly as he delayed their game.

That may have been the low point as Bush began five hard days of campaigning here this week in the hope of cutting into Reagan's acknowledged lead. But Bush's performance has been uneven here during appearances in Houston and Dallas. At his best he is crisp and sure, at his worst he garbles his easiest applause lines. Today, at a luncheon speech to the Dallas County Republican Men's Club, he called President Carter's failed rescue mission in Iran "divisive" rather than "decisive," and spoke of the invasion of "Russia" when he meant to say Afghanistan.

Reagan swept Texas in 1976, taking all 100 delegates that from year incumbent President Ford in a state primary campaign that saw the Panama Canal emerge is one of the great issues.

There is nothing so stirring here this year and Reagan isn't likely to make a clean sweep of the 80 delegates at stake. Bush is competitive in only about five or six of the state's 24 congressional districts, but there is some sign that the Reagan campaign has begun to take Bush's effort here more seriously since Reagan's loss in Pennsylvania.

Reagan this week canceled a scheduled stop in Abilene and added several events in the Dallas-Fort Worth area, where Bush is working hard.

The primary here has entered its third phase. The first phase was before Texan John Connally's campaign fizzled, when everyone thought the battle for Texas could be decisive in the GOP race. Phase two began in March, when Reagan's bandwagon started to roll and Connally returned to Texas "to lick his wounds" as his old antagonist Leon Jaworski, the former Watergate special prosecutor and Bush supporter, put it the other day. fPhrase three started last week, after Bush scored his victory in pennsylvania.

Don't be misled. Phase three is still decidedly lackluster -- a limited fight based on imported issues and images. The issue for Bush is Reagan, and the vehicles for attack are the economy and foreign policy. But Bush spends as much time telling people that he plans to emphasize his differences with Reagan as he does spelling out those differences.

On economics, the principal disagreement is over how strongly Reagan worships at the altar of Kemp-Roth, the proposal to cut taxes 30 percent over three years. Bush says it would result in 30 percent inflation and opposes it, calling instead for a more limited tax cut and reductions in federal spending.

On foreign policy, he knocks Reagan for inexperience. "We cannot take a chance on another president who has absolutely no experience whatever in foreign affairs," Bush told a rally in Houston Monday night.

But, like Reagan, he calls for a tough foreign policy and his principal difference seems to be that he would provide experienced toughness against Reagan's inexperienced toughness. On Monday, he endorsed the failed Iranian rescue mission, blasted Carter's "weakness and vacillation" on foreign policy and called Secretary of State Cyrus R. Vance's resignation "correct" though he disagreed with Vance's reasons for quitting. Today he blamed both Carter and U.S. allies for the allies' failure to fully support this nation on a variety of issues.