JERUSALEM (Reuters) - Prime Minister Benjamin Netanyahu’s toughest rival in Israel’s April election, a popular former general, made strong gains on Wednesday in the first opinion polls released after his inaugural campaign speech.

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But in a multi-party contest whose ultimate winner has always been determined in Israel by post-election wheeling and dealing, Netanyahu is still on course to build a right-wing coalition in parliament similar to the one he now heads, according to commentary accompanying the surveys.

In a long-awaited speech on Tuesday that broke his silence since joining the campaign, former military chief Benny Gantz criticized what he termed a leadership detached from the people and too concerned with hanging onto power.

Four opinion polls on Israeli TV and news websites on Wednesday showed popularity spike for Gantz’s new middle-of-the-road Resilience party at the expense of center-left rivals. But it was still running second to Netanyahu’s right-wing Likud.

The surveys gave Gantz’s party between 19 and 24 seats in the 120-member parliament - up from around 12 to 15 in previous polls - compared with 29 to 31 for Likud, about the same number as in earlier forecasts.

Political commentators have described Gantz as the first candidate in years that voters could regard as a match for Netanyahu, now in his fourth term as prime minister, in terms of security expertise.

In his speech on Tuesday, Gantz highlighted his military record and spoke mainly in generalities about policies he intends to pursue, pledging to be tough on security while striving to pursue peace.

Yaron Dekel, a political analyst, said on Israel’s Channel 13 that if Gantz maintains his momentum and Likud’s polling numbers drop to around 28 seats, Israelis will be able to say, “Hang on, here’s a fight we’ve never seen before’”.

Much could depend, commentators said, on whether Gantz and center-left parties can agree on an alliance and subsequently attract enough voter support to form a parliamentary bloc larger than a Likud-led coalition.

Netanyahu’s legal troubles are also a wildcard: Israel’s attorney general is presently weighing whether to charge him in three corruption cases, pending pre-trial hearings. His decision is widely seen as likely to be announced before balloting on April 9.

Netanyahu has denied any wrongdoing.

Even if Likud comes out on top in the voting, some political commentators said, potential coalition members might balk at partnering with a prime minister facing a criminal trial.