The folks at the Republican Senatorial Campaign Committee are frustrated. Their polls show Sen. Lloyd Bentsen (D-Tex.) would be vulnerable to a strong Republican challenger this year. But they can't convince the Texas business and money establishment that Bentsen has done anything that deserves defeat.

They went so far as to spread the word in Dallas financial circles that Bentsen had voted for food stamps, CETA public-service jobs, legal and abortion services for the poor and other bleeding-heart liberal stuff like that. They produced a flurry of inquiring phone calls that annoyed Bentsen's staff to the point that a Bentsen aide called the Republicans to point out that the GOP Senate campaign committee chairman, Bob Packwood of Oregon, had voted for most of the same things. But the GOP failed in its mission of stirring the Texas establishment into a holy crusade to beat Bentsen.

It's no wonder the Republicans have a problem. When Congressional Quarterly published its "presidential support" scorecard last week, showing how often each member of Congress had backed Ronald Reagan's position on the 1981 roll calls, it was hard to tell who was the champion Reaganite in Texas.

Sen. John G. Tower, the staunch GOP conservative, backed Reagan on 75 percent of the roll calls. And Lloyd Bentsen, the man the Republicans would love to beat, backed Reagan 70 percent of the time.

True, those percentages can be misleading, because all votes--vital or routine--count equally. But on the 11 roll calls CQ rated as "key" tests of Reagan's program, Bentsen voted seven times with Reagan and his colleague Tower.

Bentsen may be a particularly dramatic case of political adaptation. He supported Reagan's positions in 1981 almost exactly as consistently as he had supported Jimmy Carter's positions in 1980. But he is certainly not unique. Of the 20 Democratic senators up for re- election this year, 13 voted with Reagan on half or more of their roll calls.

Three of the 13--John Stennis of Mississippi, Edward Zorinsky of Nebraska and John Melcher of Montana -- gave Reagan a higher ratio of support than they had given Carter in 1980.

The only Democratic senators running this year who opposed Reagan more often than they backed him on the CQ scorecard are the heart of the liberal lineup: Kennedy of Massachusetts, Riegle of Michigan, Metzenbaum of Ohio and Sarbanes of Maryland, most conspicuously; and, by lesser ratios, Williams of New Jersey, Moynihan of New York and Mitchell of Maine.

What this suggests to me is that most of the Democratic senators up this year have put themselves in a position where they can run a "Chuck Robb campaign" in November if conditions dictate. Robb won the Virginia governorship from the Republicans two months ago by emphasizing his broad agreement with Reagan before conservatives, and his selective disagreements when he was talking to black and liberal audiences.

Robb did that because Reagan is popular in Virginia, as he is in Arizona, Florida, Mississippi, Montana, Nebraska, Nevada, North Dakota, Tennessee, Texas, Washington and Wisconsin, to mention some of the states where Democratic senators seem to be preparing similar campaigns.

There are roughly 100 House Democrats who have constructed the same kind of records. They include Majority Leader Jim Wright of Texas, Whip Tom Foley of Washington, Chief Deputy Whip Bill Alexander of Arkansas, Caucus Chairman Gillis Long of Louisiana and key committee chairmen Jim Jones of Oklahoma, Dan Rostenkowski of Illinois and Morris K. Udall of Arizona.

Despite their publicized differences with Reagan on specific issues, all of these gentlemen voted more often with the president than against him, according to the CQ scorecard.

In taking out some "Reagan insurance" by carefully avoiding the obstructionist label, these and other less-publicized Democrats have made it harder for their 1982 Republican opponents to use the president's popularity as a weapon to club them into involuntary retirement.

If Reagan's economics fail and his popularity fades, as recent polls suggest it may be doing, these Democrats will have plenty of time to rewrite their records and start acting more like a political opposition. Last year, they preferred being safe to being brave. to use the president's popularity as a weapon to club them into involuntary retirement.

If Reagan's economics fail and his popularity fades, as recent polls suggest it may be doing, these Democrats will have plenty of time to rewrite their records and start acting more like a political opposition. Last year, they preferred being safe to being brave.