Like an octopus slowly flexing its tentacles, Congress is moving to expand the boundaries of the U.S. Capitol grounds.

A House Public Works subcommittee has approved a bill authorizing $24.3 million to buy land tracts totaling about 10 acres to the east and south of the present Capitol boundaries.

The House has no formal plans for building new office space, but with members' complaints growing about crowded quarters, the new land would provide ideal terrain for future construction.

Rep. Elliott H. Levitas (D-Ga.), chairman of the subcommittee and main sponsor of the bill, described the land acquisition as "a defensive thing" to prevent commercial development on land Congress might someday want for building.

The Levitas bill authorizes $23.7 million for the Capitol architect to purchase five tracts now in public and private hands between the Rayburn House Office Building and the Capitol power plant to the south.

Those tracts comprise 9.6 acres of land, all of which are likely to be included within Capitol-grounds boundaries envisioned in a master plan being developed by Capitol architect George M. White.

One tract, owned privately, involves about two-thirds of a city block on E Street SE, across from the power plant. Other properties ticketed for purchase -- several vacant and several leased by Congress for parking -- are owned by the District of Columbia government and the Redevelopment Land Agency.

The legislation also authorizes a $645,000 expenditure to purchase another third of an acre at the corner of Third and A streets, NE, a block east of the Supreme Court. The land, owned by the Marlow Coal Co., is leased by the court as parking space.

Another upshot of the bill, should it become law, would be the forced removal of dozens of food and souvenir vendors who create a summer bazaar atmosphere at the foot of Capitol Hill.

Segments of Pennsylvania, Maryland, Independence and Constitution Avenues, now in D.C. jurisdiction at the base of the hill, would become part of the Capitol grounds under the legislation.

Ben Wimberly, counsel for architect White, said the laws governing the Capitol grounds prohibited commerce of the type involving the truck and cart vendors. The bill would give them a year to vacate their sales places.

Wimberly said that many consider the view of the trucks, carts and tourist buses that assemble at the foot of the hill "tacky," although their removal is not the purpose of the legislation.

He said the bill, giving U.S. Capitol police control over a number of other streets bordering the Capitol grounds, is an effort to eliminate confusion and "regularize" jurisdiction now held by D.C. police.

Levitas also rejected the idea that the bill was aimed specifically at the vendors, or at further limiting political demonstrators' access to the Capitol grounds.

But, he said, "The beautiful view of the Capitol from the Mall has been somewhat deteriorated with the vendors and buses assembled there."

"It is too early to say how the land might be used," Levitas said, "but if we don't buy it now, the cost might be prohibitive at a time it is needed."