A U.S.-trained economist became Poland's new finance minister Friday, assuring he would follow the pro-market policies of his predecessor, but could push for more reforms in public spending and taxes.

Pawel Wojciechowski, 46, who has served for the past half-year as Prime Minister Kazimierz Marcinkiewicz's financial adviser, said after his official appointment that the country's economic "direction has been indicated, and will be continued."

"The most important thing is that Poland and its economy continue to grow quickly, or even faster," he said. "At the same time, this is a moment to introduce essential structural reforms, such as tax reform and public finance reform."

Wojciechowski replaces Zyta Gilowska, who resigned Thursday after a prosecutor asked a court to investigate whether she collaborated with the country's communist-era secret police. She has denied the allegations, calling them a political ploy to push her from office.

Justice Minister Zbigniew Ziobro ordered an investigation into the accusations at the request of Gilowska, who called the charges against her "blackmail," the PAP news agency reported.

Marcinkiewicz thanked Gilowska for her "very effective" work, but said he was "very happy" Wojciechowski had taken the post.

"Your preparation, acquired in business and elsewhere, including the United States ... will be very useful to Poland," Marcinkiewicz told Wojciechowski.

President Lech Kaczynski congratulated Wojciechowski on his new post, and also assured that the Cabinet change would "have no negative impact on the Polish economy."

Poland's economy grew 3.2 percent last year, and was expected to continue expanding. Standard & Poor's forecast a yearly growth average of 4.3 percent in 2006-2009. Despite the positive trend, Poland is still struggling with a 16.5 percent unemployment rate — the highest in the European Union.

Gilowska, a 56-year-old independent who also was a deputy prime minister, was seen as the key guarantor of fiscal responsibility in Marcinkiewicz's government, a coalition of his socially conservative Law and Justice party with two small Euro-skeptic groups.

The three parties favor increasing state welfare spending — a stance that economists say will overburden the country, already struggling under a high deficit. Gilowska kept that tendency in check.

Though Wojciechowski also favors market-friendly policies, analysts worry that he will lack Gilowska's domestic clout, which had helped her keep spending in line.

The sudden change also adds to ongoing political instability that threatens to make this ex-communist country, which joined the EU in 2004, less appealing to investors. Wojciechowski becomes the government's third finance minister since it took office Oct. 31.

Gilowska replaced Teresa Lubinska, a finance professor who had publicly railed against foreign investment in Poland and was fired in January.