Sen. John Culver is using a risky reelection strategy, trumpeting opposition to "reckless" defense spending and parading support for free-choice abortion while fellow endangered liberals in neighboring Midwest states dilute their ideology.

The risk in Culver's strategy: It is a high-decible replica of the campaign in this moderately conservative state that sent fellow liberal Democratic senator, Dick Clark, to humiliating defeat last fall. Clark's most publicized service to Iowa was hamstringing the United States in blocking the Soviet African offensive. Iowans were not impressed.

But tough-talking Culver, who is sharper and infinitely more effective than soft-spoken Clark, is now embarked on a suspiciously similar course. He is going all-out asking Iowans to back him as a leader of the Senate's peace bloc holding down defense spending and pushing the new Strategic Arms Limitation Treaty (SALT II). In a major race critical to control of the Senate, Culver is flying his true colors.

An early exhibit of Culver's style was on display at a well-attended dinner of the Hamilton County Democratic Finance Committee in Webster City. Striking the podium with the flat of his hand, the pugnacious former Harvard fullback hit the line: "Reckless, excessive, unnecessary defense spending" is demanded by defense-oriented senators in return for SALT II.

Promoters of bigger strategic-nuclear programs to minimize a growing first-strike Soviet margin could "mislead" the Russians about U.S. power and "invite the holocaust."

Culver appears to believe his own rhetoric. Nevertheless, some in the audience were surprised at his vehemence. "SALT isn't an issue here, at least not yet," a leading Iowa Democrat told us. As Clark before him came back to Iowa revving up right-wing fury by playing master of the Carter administration's discredited African policy and lost to conservative Republican Roger Jepsen, Culver risks similar rough treatment in 1980 because of national security questions.

Culver carries many of the same burdens that weighed down Clark. Like Clark, Culver seeks to set a precedent as the first Iowa Democrat ever elected to two successive Senate terms. Like Clark, Culver is vulnerable to attack from a well-organized, well-financed single-issue constituency that helped beat Clark: the anti-abortion lobby.

Culver is on the 1980 hit list of the National Conservative Political Action Committee (NCPAC), along with four other liberal Democratic senators: George McGovern, Alan Cranston, Frank Church and Birch Bayh. But unlike Culver, the others on the receiving end of a special $700,000 NCPAC execution fund are trying to dilute some liberal positions.

McGovern and Church, for example, both strayed from the liberal path last April in Senate votes onthe school-prayer issue. Besides hedging on SALT, Church has also gone the conservative route on votes to limit the federal budget deficit. Not so Culver.

"I am not running for reelection to walk away from a 15-year record," he told the Webster City dinner, then fired a broadside at NCPAC and "the fear-brokers peddling their wares." Two days later, addressing the Iowa Federation of Labor, Culver contrasted his strategy of parading his liberal voting record and attacking the right wing to what he called the "half-hearted effort" of liberals defeated in 1978 and their strategy of "hunkering down in the foxholes."

Culver is betting everything that his combative style and personality, with a cutting edge far sharper than Dick Clark's, will overpower the Republicans (whether conservative Rep. Charles Grassley or moderate Des Moines businessman Tom Stoner is the nominee).

That may be his best bet, but polls show that Culver has not developed a clear political personality during five years in the Senate and 10 in the House. A Des Moines Register poll last spring (that gave Culver only a 38 percent approval rating) shocked politicians by showing that 51 percent of all voters could not say whether they approved or disapproved of his Senate record.

That prompts the Republican attack on him: too close to Sen. Edward M. Kennedy (dating back to Harvard); tied to big labor; eastern oriented; not in touch with the voters of Iowa.

In response, to offset his attack on defense spending, Culver cites his record of 39 months in the Marine Corps -- then adds the throwaway line: "I never bumped into Tommy Stoner or Chuck Grassley in the Marines."

That is vintage Culver, making the point that neither potential Republican opponent served in uniform. Like his basic attack strategy, it is high-risk politics capable of backfire.