The growing level of unease within her own party over Prime Minister Margaret Thatcher's hard-line economic policies rose another notch this week, keeping pace with increases in the unemployment rate and the opposition's standing in opinion polls.

The latest attack on Thatcher from within, following the party's poor showing in county elections two weeks ago, is the formation of a new splinter group, called Conservative Center Forward, by several dozen Conservative members of Parliament.

In a scathing speech tonight at Oxford University, Francis Pym, Thatcher's former foreign secretary and the new group's chairman, charged her government with having "imprisoned itself in an ideological straitjacket."

He accused the Thatcherites of "throwing the baby out with the bath water" in their zeal to overturn the 1970s policies of the opposition Labor Party. Noting that unemployment has nearly tripled since Thatcher took over in 1979, he said the country's economic recovery "literally does not exist" for most Britons.

The new group has called for increased public spending and an "industrial strategy" that allows for more government intervention in pursuit of jobs and higher competitiveness for British industry -- all anathema to Thatcher's free-market, private enterprise policies.

Such outspoken dissent is normally the province of Labor, whose militant leftists do frequent public battle with the party's more subdued center-left. Pym tempered his remarks with opening and closing statements saying members of his group were not "disloyal" and disagreed not with Thatcher's objectives, but with her strategy.

Thatcher has appeared undeterred by opposition from outside the party, and she and her spokesmen tend to respond to internal dissent by ridiculing or ignoring it. Asked in Parliament today to repudiate the new group, Thatcher quoted one line from Pym calling the Labor Party "antidemocratic," and said she "heartily agreed."

Pym and most of the other members of the group, including former Conservative defense minister Ian Gilmour, are well-known "wets," or members of the Conservatives' moderate parliamentary wing. Neither they nor the split opposition now appears in a position seriously to interfere with Thatcher's plans for a third term victory in general elections that will be held by the autumn of 1988.

But the public nature of their assault has raised the stakes of the challenge, and coincides with a number of other long-term negative indicators that are beginning to converge.

Chief among them is the persistent problem of unemployment, now at about 13 percent of the work force. Late last month, Energy Minister Peter Walker publicly chided the government for not working hard enough to decrease joblessness, leaving hard-line supporters of Thatcher to demand his resignation for disloyalty, and party leaders uncomfortably to defend his diligence.

According to the Gallup Poll's April Political Index, 80 percent of Britons consider unemployment the country's most urgent problem, and a plurality said Labor was best able to deal with it. Only 38 percent said they were satisfied with Thatcher as prime minister. Echoing other recent surveys, Gallup showed voting support for Labor to be several points higher than for the Conservatives.