President Carter's Pattonesque rhetoric about beefing up U.S. defenses in response to the Soviet takeover of Afghanistan is being undermined by his failure to follow through where it counts: persuading Congress, his European allies and the Kremlin that he means business.

They all have reason for skepticism. Not only is his much-ballyhooed "Caribbean Task Force" looking like a seagoing Potemkin village; the ostensibly far more serious Rapid Deployment Force is underfunded. Failure to request adequate manpower and aircraft makes the Carter Doctrine to defend the Persian Gulf so much rhetoric. The question naturally arises: is the electioneering president playing games with defenses?

The seeds of disillusion with the Carter Doctrine were revealed to one high-level U.S. official in a private strategy symposium with top NATO allies in Europe last week. "They think we are running off half-cocked," this official told us, "and they may end up afraid to get involved with us." If the Kremlin shares that same suspicion about Carter's commitment, dangerous tests lie ahead for this nation.

There may be some validity to Sen. Edward Kennedy's campaign blast blaming Afghanistan on Carter's failure to carry out his public threat against the Soviet combat brigade in Cuba. There are similar possibilities for disaster lurking in the new Carter defense budget.

That budget, touted as a first step back toward marching Soviet power, asks the ridiculous grand total of $514,000 for Carter's "Caribbean Task Force." Supposedly designed to prevent Soviet-Cuban machinations in the Carribean, the task force was announced by Carter almost four months ago. To date, it has no operational control over any military or naval units. a

Members of Congress specializing on the defense budget write off the Caribbean Task Force as whimsy. But they worry about what the president really has in mind for his presumably serious Rapid Deployment Force, an integral part of the anti-Soviet Persian Gulf defense. Yet the fine print in the new budget raises anxious eyebrows whether the RDF is more gamesmanship.

For the fiscal year starting next Sept. 1, the president does not ask one cent for higher Army or Marine Corps manpower levels, presumably a prerequisite for any meaningful Rapid Deployment Force. The new budget seeks no major new appropriations to modernize airlift and sealift to move men and supplies; it would fund only a limited number of new ships and planes that could not be ready for years.

When sharp-eyed military bureaucrats in the Kremlin focus on a new U.S. "doctrine" that undertakes full defense of the entire Persian Gulf region, they read the fine print. U.S. allies have been victimized in the past by sudden Carter switches, as when he abruptly canceled the neutron warhead. So this time they too read the fine print under large promises. Today, neither the Russians nor U.S. allies pretend to know where Carter is leading.

Military budget specialists in Congress are also in the dark, raising the possibility of a defense explosion on Capitol Hill. "After the Soviet invasion of Afghanistan, the rhetoric transmitting the budget has been changed to make the president sound tougher," Rep. Delbert Latta of Ohio, senior Republican on the House Budget Committee, wrote in an official report. "But the defense budget has remained about what it would have been without the rhetoric." Latta's views might be dismissed as election-year partisanship, but they are shared privately by many Democratic colleagues.

Some White House and Pentagon aides insist Carter's commitment to post-Afghan preparedness is real but ineffective. The problem, they claim, is found in what one presidential aide calls "the small-bookkeeper mentality in the OMB [Office of Management and Budget]."

OMB Director James McIntyre has consistently (critics say deliberately) underestimated fuel costs for Air Force planes, Navy ships and Army tanks. With the price of oil pegged in September 1979 by the OMB at $24 a barrel for all of 1980, the actual price of $42 has forced Carter to seek repeated supplemental appropriations. These higher costs, while looking like good-faith follow-through on the post-Afghanistan spending increase, simply add to Carter's budget deficit while adding not a cent to military power.

Power means new aircraft, but Carter's January 1979 estimates of sophisticated planes he wanted budgeted for the Air Force in fiscal year 1981 numbered 363. When he sent his actual 1981 budget to Capitol Hill a few weeks ago, the number had dropped to 282. Army and Navy aircraft suffered similar declines.

No wonder the president, though sounding like George Patton, brings skeptical scrutiny in Western Europe, in the Kremlin and on Capitol Hill. Carter may really mean what he says about a military buildup to meet the harshest challenge since World War II, but he is not yet close to proving it.